Chapter 18 Test Flashcards Preview

AP Chemistry > Chapter 18 Test > Flashcards

Flashcards in Chapter 18 Test Deck (25)
Loading flashcards...
1
Q

When butane burns, 2 molecules of butane react with 13 molecules of oxygen to produce 8 molecules of carbon dioxide and 10 molecules of water. In other words, 15 molecules are converted into 18 molecules. This reaction gives off a great deal of heat, meaning that the reactants are higher in energy than the products. What drives this reaction?

A

both disorder and energy

2
Q

Look at the butane and oxygen reaction.

Which statement about this reaction is not correct?

A

If the reverse reaction occurred, it would violate the first law of thermodynamics.

3
Q

Look at the decomposition reaction for sodium bicarbonate
2NaHCO3(s) <==> Na2CO3(s) + H2O(g) + CO2(g)
Suppose that ΔH = 64.5 kJ/mol and ΔS = 0.167 kJ/mol*K. Which statement about this reaction is correct? Assume that ΔH and ΔS are constant for all the given temperatures

A

The reaction is at equilibrium at about 386 K

4
Q

Look at the fusion of water reaction.
H2O(l) <==> H2O(s)
At 273K, ΔH = -6,007 J/mol and ΔS = -22.0 J/mol*K. Suppose that we increase the temperature from 273 K to 283 K. Find the value for ΔG at 283 K and also tell whether the reaction is spontaneous at 283 K, nonspontaneous at 283 K, or at equilibrium

A

ΔG = 219 J / mol. The reaction is nonspontaneous at 283 K.

5
Q

Look at the following reaction
2SO3(g) <==> 2SO2(g) + O2(g)

Suppose that you are given the following information for this reaction at room temperature
ΔG°f for SO2(g) = -300.19 kJ/mol
ΔG°f for O2(g) = 0.0 kJ/mol
ΔG°f for SO3 = -371.1 kJ/mol

Find the value for ΔG° for this reaction and state whether the forward reaction is spontaneous, nonspontaneous, or at equilibrium

A

ΔG° = 141.8 kJ / mol. The forward reaction is nonspontaneous.

6
Q

Calculate the standard entropy change at 25°C for the formation reaction shown below
Pb(s) + O2(g) <==> PbO2(s)

S° = 64.81 J/mol*K for Pb(s) at 25°C
S° = 205.3 J/mol*K for O2(g) at 25°C
S° = 68.7 J/mol*K for PbO2(s) at 25°C
A

−201.4 J / mol • K

7
Q
What is the value of Keq at 375 K for the following reaction?
3NO(g) <==> N2O(g) + NO2(g)
Keq = 1.8*10^8 (at 298K), 
ΔH° = -155 kJ/mol, ΔS < 0,
and R = 8.31 J/mol*K
A

4.7 × 10^12

8
Q

Look at the graph for Keq vs. T for an endothermic reaction and an exothermic reaction.

Which of the following statements about these plots is not correct?

A

Actual Keq values can be determined from this graph.

9
Q

Suppose that ΔG°NOBr = 82.42 kJ/mol,
ΔG°NO = 86.55 kJ/mol, and
ΔG°Br2 = 3.14 kJ/mol

Suppose also that we have the following initial partial pressures at 298 K:
PNOBr = 0.9 atm, PBr2 = 0.18 atm, PBNO = 0.4 atm, and that R - 8.31*10^-3 kJ.mol
What are the values for ΔG° and Q for this reaction?

A
ΔG° = 5.70 kJ / mol;
Q = 0.19
10
Q

What is entropy?

A

a thermodynamic quantity that is a measure of the randomness or disorder in a system

11
Q

Which of the following is the definition of enthalpy?

A

Enthalpy is the stored energy in a substance that is exchanged as heat during a reaction (at constant pressure).

12
Q

Look at the plot for entropy versus temperature.

Which of the following describes Range B?

A

the entropy of fusion

13
Q

At what temperature does ΔH = TΔS for the phase change of liquid water to gaseous water at 1 atm?

A

373 K

14
Q

Spontaneous processes can be driven by a decrease in energy, or by _____.

A

an increase in disorder

15
Q

Which of the following is a spontaneous process?

A

freezing of water at −24°C

16
Q

For a certain system at equilibrium, ΔS < 0. What must also be true?

A

q < 0

17
Q

Which of the following drives entropy changes?

A

statistics

18
Q

Suppose that, instead of having two connected bulbs, you have three connected bulbs. Assume that you start with the valve closed, add some gas molecules to one bulb, and then remove the valve. Which of the following shows the correct expression for the probability of finding all the gas molecules in one container after 1 hour?

A

probability = (1/3)x, where x = the number of molecules

19
Q

The reaction between hydrogen gas and oxygen gas to produce water is very exothermic, and equilibrium lies very far to the right. Which of the following describes ΔG for this reaction at equilibrium?

A

ΔG = 0 kJ/mol

20
Q

A spontaneous process is a process that____________________

A

occurs by itself without any intervention.

21
Q

Which of the following is an example of a spontaneous event that is not caused by gravity?

A

the evaporation of lake water

22
Q

Which statement defines the first law of thermodynamics?

A

The total energy of the universe is constant

23
Q

Which of the following is a nonspontaneous event?

A

a wheelbarrow being moved from one place to another

24
Q

Which statement does not pertain directly to entropy and the second law of thermodynamics?

A

The energy of the universe is conserved.

25
Q

Look at the balance analogy for two different points in a chemical reaction.

Which of the following statements best explains what happens in this reaction?

A

The system heavily favors the reactants, but it must shift slightly toward the products in order to accommodate the energy (represented by the stopper (black box)).

Decks in AP Chemistry Class (338):