Answer:
4 I believe is false and 5 is D I think
Answer:
4.) A. (TRUE)
5.) B. (THE WEATHER AND CLIMATE)
Explanation:
I HOPE IT HELPS YOU;)
Which energy profile best shows that the formation of NO2 requires 33.1
kJ/mol?
The energy profile representing the reaction of the formation of NO2 is energy profile B; option D.
What is an energy profile diagram?An energy profile diagram is a diagram which illustrates in the form of a graph the energy changes that occur as reactant molecules react to form products.
An energy profile has energy of the molecules plotted on the y-axis and the reaction pathway or the reaction progress on the x-axis.
The shape of an energy profile depends on whether the reaction is an endothermic or exothermic reaction.
An exothermic reaction will have the energy of reactants higher than that of products, whereas an endothermic reaction will have the energy of products higher than the reactants.
The formation of NO2 is an endothermic reaction which requires 33.1kJ/mol of energy to complete.
Therefore, the energy profile representing the reaction is energy profile B.
In conclusion, an energy profile diagram shows energy changes that occur in a reaction graphically.
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You want to control the temperature of an enzyme-controlled reaction that is taking place inside a flask. What is the most effective way to keep the reaction at a controlled and steady temperature?
Use of thermostat is the most effective way to keep the reaction at a control temperature.
What is the most effective way to keep the reaction in control?The reaction takes place in a thermostat is the most effective way to keep the reaction at a controlled and steady temperature because thermostat regulates the temperature of that solution which is placed in it. If the temperature goes higher then the extra heat is released from the system.
So we can conclude that use of thermostat is the most effective way to keep the reaction at a control temperature.
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Hydrogen gas and oxygen gas react to produce water. Both of these gases are present in
the air around us -so, how come water isn't being produced all around u?
Water isn't being produced all around us because the hydrogen and oxygen are present in stable form.
How come water isn't being produced all around us?Water molecule is produced when the unstable hydrogen reacts with unstable oxygen because they are very reactive. Due to their reactive nature, hydrogen and oxygen react with each other forming water molecule. So that's why we can say that water is not being produced around us due to stable form of hydrogen and oxygen.
So we can conclude that Water isn't being produced all around us because the hydrogen and oxygen are present in stable form.
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Why are pure liquids and solids not included in the reaction quotient or the equilibrium constant expression for a given heterogeneous reaction
Pure liquids and solids at the equilibrium stage:
Pure solids and pure liquids are not included in expressions for the equilibrium constant of heterogeneous equilibria since their concentrations are constant across time. Therefore, including it in our equilibrium expression is not significant.
Equilibrium expression:
When a certain chemical reaction is in equilibrium, the rates of the forward and backward reactions are equal, which means that there is no net change in the concentrations of the reactants and products and that the reaction mixture's composition does not change.
The concentration of solid and liquid:
Solid or liquid concentration,
= No. of Moles/ Volume in L
= Mass/(Volume × molar mass)
= Density/ Molar mass
Pure solids and liquids have constant densities and molar masses at a constant temperature.
Because of this, they have constant molar concentrations, which means that they are not considered in the equilibrium constant for a heterogeneous reaction.
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Which of these is an example of investigating an intensive property?
Oweighing sand in a bag
Omeasuring the length of wire
O determining if a rock is magnetic
Orecording the volume of water in a cylinder
An example of investigating an intensive property is determining if a rock is magnetic. That is option C.
What is intensive property?Intensive property is defined as the property of a substance that doesn't rely on the amount of the substance.
Examples of Intensive property include:
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What is the energy of a photon emitted with a wavelength of 448 nm?
According to the Planck-Einstein relation, the energy of a photon emitted with a wavelength of 448 nm is 4.44 × 10⁻¹⁹ J.
What is a photon?A photon is a particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass.
Step 1. Calculate the frequency of the photon.A photon is emitted with a wavelength (λ) of 448 nm. Given the speed of light (c) is 3.00 × 10⁸ m/s, we can calculate the frequency (ν) of the photon using the following expression.
ν = c/λ
ν = (3.00 × 10⁸ m/s ) / (4.48 × 10⁻⁷ m) = 6.70 × 10¹⁴ s⁻¹
Step 2. Calculate the energy (E) of the photon.We will use the Planck-Einstein relation, being Planck's constant h = 6.63 × 10⁻³⁴ J.s.
E = h × ν
E = (6.63 × 10⁻³⁴ J.s) × (6.70 × 10¹⁴ s⁻¹) = 4.44 × 10⁻¹⁹ J
According to the Planck-Einstein relation, the energy of a photon emitted with a wavelength of 448 nm is 4.44 × 10⁻¹⁹ J.
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Two balloons, one containing 1.54 L hydrogen gas and the other containing 0.72 L of
helium gas, are at the same pressure and temperature conditions. If the second balloon
contains 0.100 mol of helium, then the mass of hydrogen gas in the first balloon is:
A. 0.43 g
B. 0.22 g
C. 0.094 g
D. 0.047 g
Answer:
A.) 0.43 g
Explanation:
Before you can calculate the mass, you need to find the moles. You can do this by using Avogadro's Law:
V₁ / n₁ = V₂ / n₂
In this equation, "V₁" and "n₁" represent the first balloon's volume and mole value. "V₂" and "n₂" represent the second balloon's volume and mole value. Since you are searching for the first balloon's mole value, you can plug the other values into the equation and simplify to find n₁.
V₁ = 1.54 L V₂ = 0.72 L
n₁ = ? moles n₂ = 0.100 moles
V₁ / n₁ = V₂ / n₂ <----- Avogadro's Law
1.54 L / n₁ = 0.72 L / 0.100 moles <----- Insert values
1.54 L / n₁ = 7.2 <----- Simplify right side
1.54 L = 7.2 x n₁ <----- Multiply both sides by n₁
0.214 = n₁ <----- Divide both sides by 7.2
Now, you can find the mass using the molar mass of the gas. Remember, hydrogen exists as a diatomic molecule.
Atomic Mass (H₂): 2(1.008 g/mol)
Molar Mass (H₂): 2.016 g/mol
0.214 moles He 2.016 g
-------------------------- x ----------------- = 0.43 g H₂
1 mole
The Neutral Gator program used methods that _____. The Neutral Gator program used methods that _____. reduced the amount of carbon dioxide already in the atmosphere decreased production of carbon dioxide increased production of carbon dioxide decreased production of carbon dioxide and reduced the amount of carbon dioxide already in the atmosphere
The Neutral Gator program used methods that reduced the amount of carbon dioxide already in the atmosphere and also helps in decreased production of carbon dioxide.
The rate of CO2 increase is in the last few hundred years is 10 times more with the rate of increase (or decrease, for that matter) in the preceding 400,000 years.
There are many possible reasons for this cause , some primary factors are listed below:
Increase in populationincreased emission of green house gases, as we all know auto mobile industry is growing rapidly and this vehicles releases harmful gases like CO2, CO ,etc. and increases carbon % , this CO2 is a main gas component in green house effect.Deforestation, as the amount of plant decreases the CO2 present in atmosphere increases, plants uses CO2 and sun lite to make their food via photosynthesis.Increased emission of Industrial flue gases, etc.Learn more about green house effect here...
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Sodium phosphate dissolves as follows: na3po4(s) → 3na (aq) po4-(aq). How many moles of na3po4 are required to make 1. 0 l of solution in which the na concentration is 0. 15 m?
The 0.05 moles of [tex]Na_{3}PO_{4}[/tex] required to make 1 L of solution in which the [tex]Na[/tex] concentration is 0. 15 M.
Calculation,
The Sodium phosphate dissolves as follows:
[tex]Na_{3}PO_{4}(s)[/tex] → [tex]3Na^{+} (aq)+PO_{4}^{-} (aq)[/tex]
To make 1. L of solution in which the [tex]Na^{+[/tex]concentration is 0. 15 M
The morality of [tex]Na^{+[/tex]= 0.15 M = number of moles / volume in lit
The morality of [tex]Na^{+[/tex]= 0.15 M = number of moles /1 Lit
number of moles of [tex]Na^{+[/tex] = 0.15 mole
The mole ratio is 1: 3
It means, the 1 mole of [tex]Na_{3}PO_{4}(s)[/tex] required to form 3 mole of [tex]Na^{+[/tex]
So, to form 0.15 mole of [tex]Na^{+[/tex] = 1×0.15 / 3 moles of [tex]Na_{3}PO_{4}(s)[/tex]required.
Hence, number of moles of [tex]Na_{3}PO_{4}(s)[/tex] required = 0.05 moles.
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How many moles of solute particles are present in 1 l (exact) of aqueous 0.057 m hno3?
The total number of moles of solute particles present in 1L (exact) of aqueous 0.057 m hno3 is 0.166 mol
Initial moles of HNO3 = 1Lx 0.083 mol HNO3/1 L
The HNO3 is a strong acid that can be completely dissociated in the following way.
HNO3→H + NO
1 mol 1 mol 1 mol
The HNO3 is dissociated into two particles (Kt and NO3). So that,
total moles particles = 0.083 mol (K) + 0.083 mol (NO) = 0.166 mol
The number of moles of solute = mass of solute ÷ molar mass of solute, where mass is measured in grams and molar mass (defined as the mass of one mole of a substance in grams) is measured in g/mol.
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This graph illustrates the course of a chemical reaction with and without an enzyme. While the products and reactants are the same, the presence of an enzyme changes the amount of energy required for the reaction to begi
Red curve shows the course of the reaction in the presence of an enzyme. Line a represents the activation energy for that reaction.
Hence, Option (iv) is correct answer.
What is Activation Energy ?Activation energy is the minimum energy required an input of energy to initiate the reaction.
[tex]k = Ae^{\frac{-E_a}{RT}}[/tex]
where,
k = rate constant
A = pre-exponential factor
Eₐ = activation energy
R = universal gas constant
T = absolute temperature (in K)
Activation energy = Threshold energy - Energy of colliding molecule.
Thus from the above conclusion we can say that Red curve shows the course of the reaction in the presence of an enzyme. Line a represents the activation energy for that reaction.
Hence, Option (iv) is correct answer.
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Disclaimer: The question was given incomplete on the portal. Here is the complete question.
Question: This graph illustrates the course of a chemical reaction with and without an enzyme. While the products and reactants are the same, the presence of an enzyme changes the amount of energy required for the reaction to begin.
Part A - Interpreting the graph
Which curve shows the course of the reaction in the presence of an enzyme--the black curve or the red curve? Which line represents the activation energy for that reaction--a, b, or c?
(i) a black curve; line a
(ii) black curve; line b
(iii) black curve; line c
(iv) red curve; line a
(v) red curve; line b
(vi) red curve; line c
Oxygen is a gas at 20 °C .
(i) Describe the arrangement and behavior of the particles in the gas.
Answer:
They are not arranged in a particular way.They have negligible intermolecular force of attraction and having more spaces between the particles.
Determine the grams of sodium chloride produced when 10.0 g of sodium react with 10 g of chlorine gas according to the equation
2na + cl2 = 2nacl
When 10.0 g of sodium react with 10 g of chlorine gas according to the equation, the mass of sodium chloride produced is 25.4 g.
Mass of sodium chloride producedThe mass of sodium chloride produced in the given reaction is calculated as follows;
2Na + Cl2 = 2Nacl
In the reaction above;
2(23 gram of sodium) -------------------- 2(58.44 g of sodium chloride)
10 g of sodium -------------------------- ? mass of sodium chloride
46 g of Na ----------------------------116.88 g of NaCl
10 g of Na ---------------------------- ? NaCl
= (10 x 116.88)/46
= 25.4 g
Thus, when 10.0 g of sodium react with 10 g of chlorine gas according to the equation, the mass of sodium chloride produced is 25.4 g.
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Which sample contains the greatest number of atoms?
(a) 27.2 g cr
(b) 55.1 g ti
(c) 205 g pb
Answer:
b option is correct
Explanation:
chegg You add a sprinkle of sugar (non-volatile solute) to a beaker of water; the vapor pressure of the solution, compared to the vapor pressure of the pure solvent before the sugar was added, will:
If a non-volatile sugar is added to water , the vapor pressure of liquid will tend to decreases and this reduction of vapor pressure is said to be proportional to the numbers of mole fraction of solute that was added to it.
What occurs when a non volatile solute is added to a solution?In the case above, the vapor pressure of the solution is known to be lowered if compared to the vapor pressure of the pure solution.
Therefore if a non-volatile solute is said to be place or added to a pure solution such as water, the vapor pressure of the solution will be reduced than that of the pure solution.
Hence, the statement that If a non-volatile sugar is added to water , the vapor pressure of liquid will tend to decreases and this reduction of vapor pressure is said to be proportional to the numbers of mole fraction of solute that was added to it is correct.
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If the concentration of the acid is represented by the variable x, then what should you use to represent the concentration of the base so you can solve for the concentrations needed to make a 0.10 M buffer
Concentration of base in terms of x is 0.1 - x.
What is Concentration?The amount of solute that has dissolved in a specific amount of solvent or solution is measured as solution concentration. A concentrated solution is one that has a significant amount of dissolved solute in it. A diluted solution is one that has a little amount of dissolved solute in it.
A 0.10M buffer solution mean the sum of concentration of acid and base in the buffer is 0.1M
if A is acid nd B is its conjugate base
[A] + [B] = 0.1
[B] = 0.1 - [A]
if [A] or acid concentration is x, [B] or base concentration is
[B] = 0.1 - x
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The gas arsine, AsH3, decomposes as follows: In an experiment at a certain temperature, pure AsH3(g) was placed in an empty, rigid, sealed flask at a pressure of 392.0 torr. After 48 hours the pressure in the flask was observed to be constant at 488.0 torr. a. Calculate the equilibrium pressure of H2(g). b. Calculate Kp for this reaction
The equilibrium pressure of [tex]H_{2}[/tex] is 288 torr. and [tex]K_{p}[/tex] for this reaction is 0.786 atm.
from the reaction:- [tex]2AsH_{3}[/tex] ⇄ [tex]2As + 3H_{2}[/tex]
initial concentration 392 torr. 0
at equilibrium. 392 - [tex]2x[/tex]. [tex]3x[/tex]
and the final pressure in the flask = 488 torr.
Hence,
[tex]( 392 - 2x ) + 3x = 488\\ x = 488-392\\x = 96 torr.[/tex]
The partial pressure of [tex]H_{2}[/tex] is 3 × 96 = 288 torr.
and [tex]AsH_{3}[/tex] is 392 - ( 2 × 96 ) = 392 - 192 = 200 torr.
Now, to find [tex]K_{p}[/tex] for this reaction, we will use [tex]K_{p} = \frac{(P_{H_{2} })^{2} }{( P_{AsH_{3} } )^{2}}[/tex]
putting all the values, we get,
[tex]K_{p} = \frac{(288)^{3} }{(200)^{2} }[/tex]
= 597.1968 torr.
= 0.786 atm. ( 1 atm = 760 torr. )
what do you mean by equilibrium?
Equilibrium in chemistry is the phase that exists when a chemical reaction and its opposite reaction happen at the same rates. This word's Latin origin dates back to the prefix aequi-, which means equal, and lbra, that indicates scale or balance.
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A 50.7 g meta l ro d is hea'ted t o 92. 3 degree s Celsius. I t is adde d t o a calorimete r fille d wit h 25.O g o f wate r a t 23. 0 degree s Celsius. Wha t is th e fina l temperatur e o f th e mixture
Answer:
Can you be more clear with your question
A certain reaction has an activation energy of 54.0 kJ/mol. As the temperature is increased from 22C to a higher temperature, the rate constant increases by a factor of 7.00. Calculate the higher temperature.
The higher temperature will be:
As the temperature is increased from 22°C to a higher temperature, the rate constant increases by a factor of 7.00. The final temperature will be 271.74K.
What is the activation energy?
Activation energy is defined as the extra energy provided required to activate the molecules to start reacting and forming intermediate and later product.
Arrhenius equations given the relation rate constant and activation energy.
[tex]LnK=Ae^{-\frac{E_a}{RT}\\\\[/tex]
Where,
K= Rate constant
A= Pre exponential factor
[tex]E_a=[/tex] Activation energy
When two rate constants are given [tex]K_1\,[/tex] and [tex]\,K_2[/tex]
[tex]ln\frac{K_2}{K_1}=\frac{E_a}{R}(\frac{1}{T_2}-\frac{1}{T_1})[/tex]
Given,
[tex]T_1[/tex] = 22°C = 295K
Rate constant[tex](K_1)[/tex] increases by a factor of 7,i.e, [tex]K_2=7K_1[/tex]
[tex]E_a[/tex]= 54 kJ/mole = 54000 J/mole
R= 8.314 [tex]J\,mol^{-1}K^{-1}[/tex]
Putting the values,
[tex]ln\frac{K_2}{K_1}=\frac{E_a}{R}(\frac{1}{T_2}-\frac{1}{T_1})[/tex]
ln 7 x 8.31454000 = (1/[tex]T_{2}\\[/tex] - 1/295)
0.299 x [tex]10^{-3}[/tex] + 1/295 = 1/[tex]T_{2}[/tex]
0.00368 = 1/[tex]T_{2}[/tex]
[tex]T_{2}[/tex] = 1/0.00368
[tex]T_{2}[/tex] = 271.74 K
Therefore,
The increase in temperature will change from 295K to 271.74K.
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A known amount of heat is transferred to a sample of iron and the iron raises its temperature by 4.0 degrees Celsius. What would be the temperature increase if the same amount of heat was transferred to the same mass of water
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Consider the balanced reaction
below:
P2O3 + 3H₂O → 2H3PO3
How many grams of diphosphorus
trioxide, P2O3, are required to produce 10.2 moles of phosphorous acid, H3PO3?
I really really need help and I’m struggling with chemistry rn
Answer:
561 g P₂O₃
Explanation:
To find the mass of P₂O₃, you need to (1) convert moles H₃PO₃ to moles P₂O₃ (via mole-to-mole ratio from equation coefficients) and then (2) convert moles P₂O₃ to grams P₂O₃ (via molar mass). It is important to arrange the ratios/conversions in a way that allows for the cancellation of units. The final answer should have 3 sig figs to match the amount of sig figs in the given value.
Atomic Mass (P): 30.974 g/mol
Atomic Mass (O): 15.998 g/mol
Molar Mass (P₂O₃): 2(30.974 g/mol) + 3(15.998 g/mol)
Molar Mass (P₂O₃): 109.942 g/mol
1 P₂O₃ + 3 H₂O -----> 2 H₃PO₃
10.2 moles H₃PO₃ 1 mole P₂O₃ 109.942 g
---------------------------- x -------------------------- x ------------------- = 561 g P₂O₃
2 moles H₃PO₃ 1 mole
The removal of one or more electrons from a neutral atom results in and
Answer:
The removal of one or more electrons from a neutral atom results in a cation.
Explanation:
When you remove electrons from a neutral atom, the atom becomes more positive. Electrons have a negative charge and the protons inside of the nucleus have a positive charge. When electrons are removed, the positive charges from the protons outweigh the negative charges. This results in a positively charged atom, called a cation.
A nuclear reaction can be controlled using which of the following?
Select one or more:
a. control rods
b.water to disperse the heat
c.large containers
d. small containers
Control rods is regarded as a substance which can control nuclear reaction and is denoted as option A.
What is Nuclear reaction?This is a type of reaction which involves the nuclei of an atom being split or joined together and is usually accompanied with a great amount of energy emitted in the form of heat.
The two types of nuclear reaction include:
Nuclear fusionNuclear fissionNuclear fusion involves the collision of two or more nuclei in other form a new atom while nuclear fission involves splitting the atoms to form other products and involves a very high amount of energy and exposure to organisms should be prevented as the radiations can alter DNA.
Control rods are commonly used in nuclear reactors and control the rate of fission in the fuel used. This is therefore the reason why it was chosen as the most appropriate choice.
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Which compound has both covalent and ionic bonds? pls give the explanation thx :)
A NH3
B Na2SO4
C CH3COOH
D NaCl
Answer:
B.) Na₂SO₄
Explanation:
Covalent bonds are bonds which involve electrons being shared between two atoms. These bonds only occur between nonmetals.
Ionic bonds are bonds which involve electrons being given or taken by two atoms. These bonds form between a metal and a nonmetal.
NH₃ contains nitrogen and hydrogen, two nonmetals. Therefore, this molecule only contains covalent bonds.
Na₂SO₄ has both covalent and ionic bonds. The covalent bonds are found within the polyatomic ion, SO₄²⁻. Sulfur and oxygen are both nonmetals, thus covalently combining. The ionic bond forms between the Na⁺ and SO₄²⁻. Sodium (Na) is a metal which wishes to give up electrons to have a complete octet. SO₄²⁻ serves as the anion which it bonds with.
CH₃COOH contains hydrogen, carbon, and oxygen. All of these are nonmetals, thus the only bonds formed are covalent.
NaCl contains sodium, a metal, and chlorine, a nonmetal. Therefore, this compound is held together by an ionic bond.
age
Which of the following has the greatest mass?
Select one:
1.0 mole of Zn
1.0 mole of Cu
1.0 mole of Fe
they all have the same mass
Answer:
Option (2)
Explanation:
Since the amount of each sample is the same, we are looking for the metal with the greatest density, which is copper.
If your client receives a letter from SilverScript requesting proof of Creditable Coverage, and the client has already submitted proof of creditable coverage with the enrollment application, they can ignore the letter.
If your client receives a letter from SilverScript requesting proof of Creditable Coverage, they can ignore the letter is a false statement
What is Creditable coverage?Creditable coverage is known to be a form of an health insurance, that consist of prescription drug and also other kinds of health benefit plan that is known to meets the minimum amount of qualifications.
Note that the types of creditable coverage plans are group and individual health plans, student health plans, and others.
It is not right to ignore any letter sent to you concerning the case above as it may be vital and as such, the statement of If your client receives a letter from SilverScript requesting proof of Creditable Coverage, and the client has already submitted proof of creditable coverage with the enrollment application, they can ignore the letter is a wrong/false statement.
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true or false, Valence bond theory states that a bond between two atoms is the strongest when the nuclei of the atoms are touching each other.
Valence bond theory stating that a bond between two atoms is the strongest when the nuclei of the atoms are touching each other is true.
What is Valence bond theory?This theory states that when two valence orbitals of two different atoms overlap on each other, the bond is usually strong.
The bond formed in this scenario is usually covalent which involves sharing of the valence electrons.
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Read the chemical equation.
n2 + 3h2
2nh3
using the volume ratio, determine how many liters of nh3 is produced if 3.6 liters of
h2 reacts with an excess of n2, if all measurements are taken at the same
temperature and pressure? (5 points)
1) 5.4 liters
2) 2.4 liters
3) 1.8 liters
4) 1.2 liters
The volume of [tex]NH_3[/tex] that will be produced is 2.4 liters. The correct option is 2.
Volume ratioThe equation of the reaction goes thus: [tex]N_2 + 3H_2 --- > 2NH_3[/tex]
The ratio of H2 to NH3 is 3:2.
Thus, with 3.6 L of H2, the volume of NH3 that will be produced is:
2/3 x 3.6 = 2.4 liters.
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generalized approach for the synthesis of silica supported pd-zn, cu-zn andni-zn gamma brass phase nanoparticles
According to the available literature, standard nanoparticle (NP) production processes make it especially challenging to reach the catalytically important and highly complicated intermetallic -brass crystal structure.
We present a straightforward and logical method for obtaining this phase in M-Zn (M = Pd, Cu, Ni) systems as silica-supported single-phase nanocrystals. This hybrid technique begins with the synthesis of supported M/SiO2 using typical methods (dry impregnation and strong electrostatic adsorption), followed by several hours of heating to high temperatures in the presence of a stoichiometric quantity of metallic Zn in an evacuated closed system.
Catalytically important bimetallic systems:Pd-Zn is by far the most common in catalytic applications and produces the smallest particle size (8 nm). We investigated the effect of various synthesis parameters on phase purity and particle size distribution in the case of synthesized -brass Pd-Zn/SiO2 supported catalysts and provided general guidelines for synthesis optimization.
Pd/SiO2 is transformed to -brass Pd-Zn/SiO2, resulting in a precipitous drop in CO adsorption and a 25 kJ/mol increase in the ethylene hydrogenation barrier, indicating that the catalytic active sites are significantly modified as a result of alloying. We anticipate that these catalysts will find use in a variety of Pd-catalyzed chemistries.
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According to the quantum mechanical model, where are electrons located?
Select one:
A. in orbits around the nucleus
B inside the nucleus
C. at great distances from the nucleus
D. in the cloud-like areas around the nucleus
Answer:
D.) in the cloud-like areas around the nucleus
Explanation:
A.) is incorrect. Electrons exist in orbitals in the Bohr's Model.
B.) is incorrect. Electrons do not exist in the nucleus. They always exist outside of the nucleus, but their exact position has been debated.
C.) is incorrect. While the electron clouds in the quantum mechanical model can cover a relatively large amount of space, the distance from the nucleus is not great. Within this cloud, electrons can exist closer to the nucleus at a particular time.
D.) is correct. Electrons are said to exist somewhere within these clouds around the nucleus. The model uses the cloud references to display how you can never be sure where the electrons are located - they are always moving around.