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Chem 152 > Chem 152 Exam 2 > Flashcards

Chem 152 Exam 2 Flashcards

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1
Q

True or False: Raising the temperature of a reaction increases the rate because the activation energy is decreased. Why?

A

False, because raising the temperature increases the rate and the activation energy.

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2
Q

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?

A

True, this is because the steps before lead to how the slow step is found.

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2
Q

True or False: The rate law for a reaction can be written directly from the balanced chemical equation. Why?

A

False,

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3
Q

True or False: Adding a catalyst to a reaction usually lowers the activation energy, thus decreasing the rate of the reaction. Why?

A

False, it can lower and raised the EA BUT it increases the rate of rxn when it is lowered.

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4
Q

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?

A

True, because with this catalyst added the reaction is sped up since the EA is lowered.

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5
Q

True or False: The half life of a first order reaction does not depend on the initial reactant concentration. Why?

A

True, the half life of a first order rxn primarily depends upon the K of a rxn.

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6
Q

True or False: Integrated rate laws show the dependence of concentration on rate. Why?

A

False, they show the dependence of concentration on TIME.

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7
Q

True or False: At equilibrium, the concentration of products and reactants no longer change. Why?

A

True, because they are at equilibrium! This literally means they can go back and forth from reactants to products and vis versa.

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7
Q

True or False: At equilibrium, the reaction completely stops. Why?

A

False, this is because they are forever turning back from products and reactants.

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8
Q

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?

A

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.

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8
Q

True or False: When the value for Kp is much smaller than I, this means products are favored at equilibrium. Why?

A

False, this is because when Kp is much smaller than I it means reactants are favored at Equilibrium.

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9
Q

True or False: The rate of a zero-order reaction is independent of the concentration of reactants. Why?

A

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.

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10
Q

True or False: In many cases, a catalyst increases the rate of a reaction by increasing the activation energy. Why?

A

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.

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10
Q

True or False: Activation energy is the minimum amount of energy required to initiate a chemical reaction. Why?

A

True, because the EA does not have to be very big, it can even be negative so it can be very minimum.

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11
Q

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?

A

False, adding a solid to gases leads to no change which means this is NOT a homogeneous catalyst.

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11
Q

True or False: The mechanism of a reaction can be known with certainty. Why?

A

False, this is because many mechanisms are difficult to calculate and can lead to mistakes easily.

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11
Q

True or False: A catalyst can increase the rate of reaction by raising the activation barrier. Why?

A

False, becuase the will lower the activation barrier

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12
Q

True or False: At equilibrium, the total concentration of products equals the total concentration of reactants, that is
[products] = [reactants]. Why?

A

False, this is false because
[reactants] = [products] and is forever interchangeable

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12
Q

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?

A

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)

13
Q

True or False: Equilibrium is the result of the termination of all chemical change. Why?

A

False, it has equal movement in both directions so chemical change happening in both directions.

13
Q

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?

A

False, C is a solid so it would not be included in an equilibrium expression.

14
Q

True or False: When equilibrium is reached, the concentrations of products and reactants remain constant. Why?

A

True, Becuase if any products or reactants were to change it would no longer be in equilibrium.

15
Q

True or False: If Q is greater than K reactants of a rxn are favored. Why?

A

True, This is because K is closer to 0 which means that the reactants are much larger than products so Q will be greater.

16
Q

What is the instantaneous rate?

A

Rate at one specific point

17
Q

How to find the instantaneous rate? (the formula)

A

Delta[Reactant]M
——————–
Delta[Time]

18
Q

What can affect rate?

A

Orientation of molecules, Catalysts lower/raise
EA only, Temperature affects k/rate ONLY.

19
Q

0,1st, or 2nd: ln(A)t vs. Time, is k + or -?

A

1st, k is -

20
Q

0,1st, or 2nd: 1/[A]t vs. Time, is k + or -?

A

2nd, k is +

21
Q

0,1st, or 2nd: [A]t vs. Time, is k + or -?

A

0, and k is -

22
Q

How do you know to use 1st order for a half life?

A

The t1/2 stays the same.

23
Q

How do you know to use 2nd order for a half life?

A

The t1/2 will get smaller for the larger initial concentration

24
Q

How do you know to use 0 order for a half life?

A

The t1/2 will get larger for the smaller initial concentration

25
Q

What is it when Qc > Kc?

A

Products are favored. Q and P are much larger while R is much smaller.

25
Q

What is it when Qc=Kc?

A

Equilibrium

26
Q

What is it when Qc < Kc?

A

Reactants are favored. Q and P are much smaller while R is much larger.

27
Q

What is a 1st order rate law?

A

Rate= k[A]

28
Q

What is a 2nd order rate law?

A

Rate= k[A]^2 OR K[A][B]

29
Q

What is a 0 order rate law?

A

Rate= k

30
Q

What is the standard notation of Equilibrium?

A

[Products]^(x)
K= ——————–
[Reactants]^(y)

31
Q

How to find Kp given Kc?

A

Kp= Kc(RT)^(f-i moles)

32
Q

How to find Kc when given Kp?

A

Kp
Kc = —————————————
(RT)^(change in f-i/moles)

33
Q

What must be true about prod and reactants at equilibrium?

A

Their concentrations don’t change

34
Q

Q relates the quantity of products to reactants at a point where the rxn is what?

A

Not necessarily at equilibrium

35
Q

What does K represent as it relates quantity of products to reactants at a point where the rxn is?

A

At equilibrium

36
Q

Positive H leads to heat being added to what? Reactants or products?

A

Reactants

37
Q

Negative H leads to heat being added to what? Reactants or products?

A

Products

Chem 152 (7 decks)

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