Chem 141 Exam 1
integrated rate law for 2nd order
1/[x] = kt +1/[x]0
Zero order reaction
A reaction was shown to have an increasing half-life with increasing concentration of reactant. What order is this reaction?
zero
A reaction was shown to have an increasing half-life with increasing concentration of reactant. What order is this reaction?
The contents of the flask are at equilibrium and no shift will occur. (do the C^c D^d thing to find out q if it equals the given kc theres no change). (The problem gave Kc = 10.5. Since Kc = Q the contents of the flask are at equilibrium and the amounts of products and reactants will not change. Note: if Kc > Q the equilibrium will shift to the right and if Kc < Q the equilibrium will shift to the left.
A sealed reaction flask contains a mixture of 0.100M CH₃OH, 0.152M CO, and 0.250M H₂ at constant temperature. Given the following reaction: CO(g) + 2H₂(g) ⇌ CH₃OH(g) and Kc = 10.5. Select the answer that best describes the state of equilibrium in the flask. A) The contents of the flask are not at equilibrium. The reaction will shift left, forming more reactants and reducing the amount of products. B) The contents of the flask are at equilibrium and no shift will occur. C) The contents of the flask are not at equilibrium. The reaction will shift right, forming more products and reducing the amount of reactants. D) The flask will form more reactants and the amount of products will stay constant. E) The flask will form more products and the amount of reactants will stay constant. +
This would require 4 molecules to collide and react simultaneously (This mechanism step indicates that 3 molecules of A and 1 molecule of B would all have to collide at the same time in the right orientation. This would be incredibly unlikely.)
A student proposes the following step of a mechanism. Why would an expert question this mechanism step? 3 A + B → 2 C
decreasing temp (A positive ΔH indicates that this is an endothermic reaction with energy being required for the forward reaction to occur. Decreasing the temperature would shift the reaction to the left to create more reactants to reach equilibrium.)
Consider the reaction below. Which of the following would increase the partial pressure of A at equilibrium? A (g) + B (g) ⇌ C (g) ΔH > 0
increasing temp (Increasing the temperature would shift the reaction to the right to create more products to reach equilibrium.)
Consider the reaction below. Which of the following would increase the partial pressure of C at equilibrium? A (g) + B (g) ⇌ C (g) ΔH > 0 A) removing B. B) increasing the temperature. C) decreasing the total pressure. D) adding a catalyst. +
-Ea/R
Considering the Arrhenius equation, what is the slope of a plot of ln k versus 1/T equal to?
D) The reaction is first order in B and third order overall.
Considering the rate law, rate = k[A]²[B], which of the following statements is correct?
kp= C^c x D^d/A^a x B^b
equation for equilibrium partial pressure
ice table and quadratic formula
equilibirum partial pressure you set up what
products/the reactions
equilibrium components are
t 1/2 = 0.693/k (t 1/2=yrs)
first order reactions for half life
integrated rate law for zero order reaction
i[X] = -kt+[X]0
=
if q ___ k then the reaction is at equilibrium
[B] = [B]₀ × e^(-kt)
integrated rate law for first order reaction
arrhenius equation
k = Ae (-Ea/RT)
first order rate law
kt=ln[XO/XT] (decomposing with a rate constant)
integrated rate law
second order kinetics means what equation
half-life for second order reactions
t 1/2 = 1/k[X]o (k=time)
divide the concentrations of the products by the concentrations of the reactants.
to find equilibrium partial pressure you
just add them
to find the activation energy of a reverse reaction you
s-1
units for the rate of a first order reaction
the rate of reaction with the -1/A or -1/B substitute in the increaing/decreasing # and multiply it by the coefficient
what do you use for a magnitude/pressure change problem
initial charge at equilibrium
what does ice stand for
first order rate law
what equation is used to determine the amount of time required for the initial concentration to decrease by 45%
integrated rate law zero order
what equation would you use? What amount of time is required for the concentration of A to decrease from 0.800 M to 0.200 M in the zero-order reaction A → B? (k = 0.0567 M*s⁻¹)
The slow step
what is the rate determining step?
firste
what reaction is s-1?
Ice then just set it up like the A^a and solve with a quadratic
what table do you set up fr equilibrium concentrations
the numbers in the problem
whats the I in Ice
the -x or +2x etc
whats the c in ice
the numbers and xs combined
whats the e in ice
second order integrated rate law
when decreasing in the second order you use the
P
when youre dealing with pressure you add a ?
activation energy
you use this equation to find what? ln(k1/k2) = Ea/R (1/t2-1/T1)
93.75%
What fraction of a reactant has been consumed after 4 half-lives in a first-order reaction?
Products (diluting the reactants changes the products)
Consider the following reaction at equilibrium: HF(aq) + H₂O(l) ⇌ H₃O⁺(aq) + F⁻(aq) If the solution is diluted two-fold, in which direction will the equilibrium shift?
product (∆H° is positive, this is an endothermic reaction and heat is a reactant. Le Chatelier's Principle states that when a reactant is added, then the equilibrium shifts toward products.)
Consider the following reaction at equilibrium: N₂O₄(g) ⇌ 2NO₂(g) The ∆H° for this reaction is > 0. If the temperature is increased by 20.0 K while the volume is kept constant, in which direction will the equilibrium shift?
no change (pressure only affects gases)
Consider the following reaction: CH₃COOH(aq) + H₂O(l) ⇌ CH₃COO⁻(aq) + H₃O⁺(aq). An increase in the pressure of the chamber where this reaction takes place will result in
A (The equilibrium constant is less than 1 for both reactions, meaning that there must be more reactants than products.)
Consider the following two reactions occurring in the same vessel: A ⇌ B, K=0.01 A ⇌ C, K=0.02 What will there be most of in solution?
heterogenous (Ni or Pd are solids, while H₂(g) is a gas and alkenes or alkynes might be liquids. Therefore the catalyst is heterogeneous with respect to the reactants.)
Organic molecules such as alkenes and alkynes undergo reaction with H₂(g) in the presence of a solid catalyst such as Ni(s) or Pd(s). This is an example of a _____ catalysis.
dividing the concentrations of the products by the concentrations of the reactants.
The equilibrium constant is calculated by
Lowers yield, increases rate of reaction
The production of ammonia from its elements (Haber-Bosch process) is exothermic. If temperature is increased, how does this affect reaction rate and yield?
provides a new mechanism for the reaction to proceed by.
The rate of a reaction increases when a catalyst has been added to the reaction mixture. The catalyst
Kp=Kc(RT)^delta n
To find Kc and Kp you use
decreases (The Arrhenius equation is k=Ae−EARTk=Ae−EART. An increase in the activation energy would result in a smaller value for the rate constant.)
What is the effect on k as the activation energy for a reaction increases?
Termolecular (The molecularity of an elementary step is determined by how many reactants are involved in the reaction. The rate determining step is Step 1 and it has three reactants and is termolecular.)
What is the molecularity of the rate-determining step in the proposed mechanism? Step 1: H2+2NO -> N2O +H2O (slow) Step 2: N2O + H2 -> N2 +H2O (fast)
First
What is the order of the reaction A → B + C when a graph of ln[A] versus time gives a straight line with a negative slope?
first
What is the order of the reaction A → B + C when a graph of ln[A] versus time gives a straight line with a negative slope?
Zero
What order of reaction has a linear curve when plotting concentration versus time?
zeroth
What order of reaction has a linear curve when plotting concentration versus time?
25% (The half-life is the time it takes for half of the material to decompose. If one half life is 60 seconds, there would be 50% left. Then another half-life of 60 seconds, there would be 25% left)
What percentage of reactant will remain after 120 seconds if the half-life is 60 seconds for a first-order reaction?
increase in NO2 (Think of the heat as a product in the equation. As the products are increased, the reaction will shift to the left to create more reactants to reach equilibrium.)
When NO₂ dimerizes (two molecules join together to form a 'dimer') into N₂O₄, an equilibrium is reached and in the process this reaction produces heat. If you increase the temperature of the chamber in which both NO₂ and N₂O₄ reside, you would observe
the rates of the forward and reverse reactions are equal.
When a system is at dynamic equilibrium,
ln([x]/[x]₀) = -kt (given on sheet)
Which equation is used to determine the amount of time required for the initial concentration to decrease by 45% if the rate constant has units of s⁻¹?
cutting the concentrations of both NOBr and NO in half.
Which of the following changes would have no effect on the equilibrium position of the reaction below? 2 NOBr (g) ⇌ 2 NO (g) + Br₂ (g) A) adding NOBr. B) removing NO C) doubling the concentration of NO at the same time as the concentration of Br₂ is cut in half. D) cutting the concentrations of both NOBr and NO in half.
C
Which of the following statements best described Le Chatelier's Principle? A) Reactions can never really reach equilibrium. B) A reaction which is at equilibrium will always try to stay at equilibrium. C) A reaction which is at equilibrium, when disturbed, will react appropriately to reestablish equilibrium. D) All reactions will eventually run to equilibrium.
initial
A0 =
as an inhibitor
Another way to describe a species that slows down the reaction rate is
what initial is going to
At=
Stay the same (KeqKeq does not change. The equilibrium constant is not dependent upon volume or pressure.)
Consider the following reaction at equilibrium: 2NO₂(g) ⇌ N₂O₄(g) The ∆H° for this reaction is < 0. If the volume of the container is decreased by ½ while the temperature is kept constant, how will K(eq) change?
stay the same (The equilibrium constant is not dependent upon concentration.)
Consider the following reaction at equilibrium: CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g) If CO(g) is removed, how will K(eq) change?
Reactants (there are more reactants than products)
Consider the following chemical reaction at equilibrium: 2NO₂(g) ⇌ N₂O₄(g) If the container's volume is increased by a factor of 2, in which direction will the equilibrium shift?
[B] = [B]₀ × e^(-kt)
Consider the following rate law: Rate = k[B] Which of the following equations could be used to find the concentration of B at some time (t) in the reaction?
Reactants (The equilibrium shifts towards the reactants. Le Chatelier's Principle states that when a reactant is removed, then the equilibrium shifts toward reactants.)
Consider the following reaction at equilibrium CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g) If CO(g) is removed, in which direction will the equilibrium shift?
The reaction will proceed towards reactants. (If Q is larger, then that means the product concentration is too high. To "fix" this, the reaction will proceed in the reverse direction, toward reactants to reach the equilibrium, K.)
If the reaction quotient (Q) is larger than the equilibrium constant (K) for a reaction then which way will the reaction proceed?
The reaction is already at equilibrium and no shift needs to take place.
For the reaction below, the concentration of HI is 0.210 M and the concentrations of H₂, and I₂ are both 0.564 M. What must happen for the reaction to reach equilibrium? 2 HI (g) ⇌ H₂ (g) + I₂ (g) Kc = 7.21
termolecular (The molecularity of an elementary step is determined by how many reactants are involved in the reaction.)
Given the following elementary reaction what is the molecularity? A + 2B → AB₂
Bimolecular (The reaction is bimolecular. Bimolecular reactions involve the collision of two atoms, molecules or ions. In this example, two HI molecules collide and react.)
Identify the molecularity of the elementary reaction below: 2HI(g)→ H₂(g) + I₂(g)
Termolecular
Identify the molecularity of the elementary reaction below: 2NO(g) + Br₂(g) → 2NOBr(g)
the reaction will proceed in the forward direction. (If the reaction quotient (Q) for a given reaction is less than the equilibrium constant (K) then the reaction will proceed in the forward direction.)
If the reaction quotient (Q) for a given reaction is less than the equilibrium constant (K) then
the reaction is at equilibrium and the reaction will proceed at equal rates in the reverse and forward direction.
If the reaction quotient (Q) is equal to the equilibrium constant (K) for a reaction then
M-1 S-1
What are the units for the rate constant of a reaction with the rate law, Rate = k[A][B]?
