Chem 152 Exam 2 Flashcards
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True or False: Raising the temperature of a reaction increases the rate because the activation energy is decreased. Why?
False, because raising the temperature increases the rate and the activation energy.
True or False: The rate law for a reaction comes from the rate determining (slow step) of the mechanism and any steps that occur
before it. Why?
True, this is because the steps before lead to how the slow step is found.
True or False: The rate law for a reaction can be written directly from the balanced chemical equation. Why?
False,
True or False: Adding a catalyst to a reaction usually lowers the activation energy, thus decreasing the rate of the reaction. Why?
False, it can lower and raised the EA BUT it increases the rate of rxn when it is lowered.
True or False: An example of the use of a homogeneous catalyst would be adding a drop of aqueous acid to a solution of an alcohol
to speed up the reaction of the alcohol. Why?
True, because with this catalyst added the reaction is sped up since the EA is lowered.
True or False: The half life of a first order reaction does not depend on the initial reactant concentration. Why?
True, the half life of a first order rxn primarily depends upon the K of a rxn.
True or False: Integrated rate laws show the dependence of concentration on rate. Why?
False, they show the dependence of concentration on TIME.
True or False: At equilibrium, the concentration of products and reactants no longer change. Why?
True, because they are at equilibrium! This literally means they can go back and forth from reactants to products and vis versa.
True or False: At equilibrium, the reaction completely stops. Why?
False, this is because they are forever turning back from products and reactants.
True or False: Consider a 1st order reaction. A plot of ln[A] vs. time will be a straight line with a slope of −k. Why?
True, this is because in the “y = mx +b” the “m”, which is the slope is -k. Y and X are already determined and B is irrelevant to the slope.
True or False: When the value for Kp is much smaller than I, this means products are favored at equilibrium. Why?
False, this is because when Kp is much smaller than I it means reactants are favored at Equilibrium.
True or False: The rate of a zero-order reaction is independent of the concentration of reactants. Why?
True, because 0 order just calculates the final concentration and time. It is a 0 rate so it doesnt need to depend on the concentration of reactants.
True or False: In many cases, a catalyst increases the rate of a reaction by increasing the activation energy. Why?
False, this is because while yes it mainly increases the rate of rxn it decreases the EA. A higher EA means a decrease in the rate.
True or False: Activation energy is the minimum amount of energy required to initiate a chemical reaction. Why?
True, because the EA does not have to be very big, it can even be negative so it can be very minimum.
True or False: The reaction rate between hydrogen gas and a solution of styrene is increased by adding a tiny amount of powdered platinum
metal on the tip of a spatula. This is an example of the use of a homogeneous catalyst. Why?
False, adding a solid to gases leads to no change which means this is NOT a homogeneous catalyst.
True or False: The mechanism of a reaction can be known with certainty. Why?
False, this is because many mechanisms are difficult to calculate and can lead to mistakes easily.
True or False: A catalyst can increase the rate of reaction by raising the activation barrier. Why?
False, becuase the will lower the activation barrier
True or False: At equilibrium, the total concentration of products equals the total concentration of reactants, that is
[products] = [reactants]. Why?
False, this is false because
[reactants] = [products] and is forever interchangeable
True or False: When the value of Kc for a reaction is small, it indicates that the equilibrium concentration of the products is small. Why?
True, this is because when reactants are much larger then the products are much smaller since they are divided by the reactants. This leads to Kc being much smaller.
[Prod]^(x)
Kc= ——————
[REACT]^(y)
True or False: Equilibrium is the result of the termination of all chemical change. Why?
False, it has equal movement in both directions so chemical change happening in both directions.
True or False: For the following reaction, the equilibrium expression is
Kc = [CO2][N2]^2
————————
[C][N2O]^2
C (s) + 2 N2O (g) ↔ CO2 (g) + 2 N2 (g). Why?
False, C is a solid so it would not be included in an equilibrium expression.
True or False: When equilibrium is reached, the concentrations of products and reactants remain constant. Why?
True, Becuase if any products or reactants were to change it would no longer be in equilibrium.
True or False: If Q is greater than K reactants of a rxn are favored. Why?
True, This is because K is closer to 0 which means that the reactants are much larger than products so Q will be greater.
What is the instantaneous rate?
Rate at one specific point
How to find the instantaneous rate? (the formula)
Delta[Reactant]M
——————–
Delta[Time]
What can affect rate?
Orientation of molecules, Catalysts lower/raise
EA only, Temperature affects k/rate ONLY.
0,1st, or 2nd: ln(A)t vs. Time, is k + or -?
1st, k is -
0,1st, or 2nd: 1/[A]t vs. Time, is k + or -?
2nd, k is +
0,1st, or 2nd: [A]t vs. Time, is k + or -?
0, and k is -
How do you know to use 1st order for a half life?
The t1/2 stays the same.
How do you know to use 2nd order for a half life?
The t1/2 will get smaller for the larger initial concentration
How do you know to use 0 order for a half life?
The t1/2 will get larger for the smaller initial concentration
What is it when Qc > Kc?
Products are favored. Q and P are much larger while R is much smaller.
What is it when Qc=Kc?
Equilibrium
What is it when Qc < Kc?
Reactants are favored. Q and P are much smaller while R is much larger.
What is a 1st order rate law?
Rate= k[A]
What is a 2nd order rate law?
Rate= k[A]^2 OR K[A][B]
What is a 0 order rate law?
Rate= k
What is the standard notation of Equilibrium?
[Products]^(x)
K= ——————–
[Reactants]^(y)
How to find Kp given Kc?
Kp= Kc(RT)^(f-i moles)
How to find Kc when given Kp?
Kp
Kc = —————————————
(RT)^(change in f-i/moles)
What must be true about prod and reactants at equilibrium?
Their concentrations don’t change
Q relates the quantity of products to reactants at a point where the rxn is what?
Not necessarily at equilibrium
What does K represent as it relates quantity of products to reactants at a point where the rxn is?
At equilibrium
Positive H leads to heat being added to what? Reactants or products?
Reactants
Negative H leads to heat being added to what? Reactants or products?
Products
