AP Chemistry Chapter 6 + 16 Test

A reaction in which heat energy is absorbed is said to be _____.

endothermic

Heat is a reactant if it is:

endothermic

A reaction in which heat energy is released is said to be _____.

exothermic

Heat is a product if it is:

exothermic

Consider the following hypothetical reaction at 310 K. Standard free energies of formation are given in parentheses. B ----------> C o ∆G = -31.4.0 kJ/mol (?) (176.4 kJ/mol) Calculate the standard free energy of formation of compound B. a. 207.8 kJ/mol b. -207.8 kJ/mol c. 145.0 kJ/mol d. -145.0 kJ/mol

A (207.8 kJ/mol)

C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l), ΔH = -1.37 × 10^3 kJ For the combustion of ethyl alcohol as described in the above equation, which of the following is true? I. The reaction is exothermic. II. The enthalpy change would be different if gaseous water were produced. III. The reaction is not an oxidation-reduction one. IV. The products of the reaction occupy a larger volume than the reactants. a) I, II b) I, II, III c) I, III, IV d) III, IV

A (I, II)

For this system at equilibrium, how will raising the temperature affect the amount of NO present? A) The amount of NO will increase. B) The amount of NO will decrease. C) The amount of NO will remain the same. D) Answer depends on K

A (The amount of NO will increase.)

Two metals of equal mass with different heat capacities are subjected to the same amount of heat. Which undergoes the smallest change in temperature? a) The metal with the higher heat capacity. b) The metal with the lower heat capacity. c) Both undergo the same change in temperature. d) You need to know the initial temperatures of the metals.

A (The metal with the higher heat capacity.)

Which of the following reactions is not thermodynamically favored at low temperatures but becomes favored as the temperature increases? A) 2 CO(g) + O2(g) ➝ 2 CO2(g) ΔH° = -566 kJ, ΔS° = -173 J/K B) 2 H2O(g) ➝ 2 H2(g) + O2(g) ΔH° = 484 kJ, ΔS°= 90.0 J/K C) 2 N2O(g) ➝ 2 N2(g) + O2(g) ΔH° = -164 kJ, ΔS° = 149 J/K D) PbCl2(s) ➝ Pb2+(aq) + 2 Cl-(aq) ΔH° = 23.4 kJ, ΔS° = -12.5 J/K

B (2 H2O(g) ➝ 2 H2(g) + O2(g) ΔH° = 484 kJ, ΔS°= 90.0 J/K)

If ΔG° for a particular reaction is equal to -45.0 kJ/mol, what is known about the equilibrium constant, K, without doing any calculations? A) K is greater than 1 B) K is less than 1 C) K is equal to 1 D) K is a negative number

B (K is less than 1)

A 100 g sample of a metal was heated to 100C° and then quickly transferred to an insulated container holding 100 g of water at 22C°. The temperature of the water rose to reach a final temperature of 35C°. Which of the following can be concluded? A. The metal temperature changed more than the water temperature did; therefore the metal lost more thermal energy than the water gained. B. The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained. C. The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water. D. The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased.

B (The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.)

A chemical reaction is most likely to be thermodynamically favored if it is accompanied by A) increasing enthalpy and increasing entropy. B) decreasing enthalpy and increasing entropy. C) increasing enthalpy and decreasing entropy. D) decreasing enthalpy and decreasing entropy.

B (decreasing enthalpy and increasing entropy.)

What is the specific heat capacity of mercury if it requires 150. J to change the temperature of 15.0 g mercury from 25.0°C to 35.0°C? a) 1.20 J/g °C b) 2.00 J/g °C c) 2.50 J/g °C d) 3.00 J/g °C

D (3.00 J/g °C)

K(s) + 1/2 Cl2(g --> KCl(s) ∆H° = −437 kJ/molrxn How much heat is released or absorbed when 0.050 mol of Cl 2 (g) is formed from KCl(s)? A. 874 kJ is released B. 437 kJ is released C. 874 kJ is absorbed D. 437 kJ is absorbed

D (437 kJ is absorbed)

For a particular chemical reaction: ΔH = 5.5 kJ and ΔS = -25 J/K Under what temperature condition is the reaction spontaneous? A) When T < -220 K. B) When T < 220 K. C) The reaction is spontaneous at all temperatures. D) The reaction is not spontaneous at any temperature.

D (The reaction is not spontaneous at any temperature. )

Given the following free energies of formation: ∆G° C2H2(g) 209.2 kJ/mol C2H6(g)-32.9 kJ/mol for the following equation at 298 K: C2H2(g) + 2 H2(g) ---> C2H6(g) A) increase in entropy B) increase in pressure C) reaction is not favored D) reaction is favored

D (reaction is favored)

Consider the reaction H2(g) + (1/2)O2(g) → H2O(l) ΔH° = -286 kJ Which of the following is true? a) The reaction is exothermic. b) The reaction is endothermic. c) The enthalpy of the products is less than that of the reactants. d) Both a and c are true.

A (The reaction is exothermic.)

It is observed that the reaction producing KCl from its elements goes essentially to completion. Which of the following is a true statement about the thermodynamic favorability of the reaction? (A) The reaction is favorable and driven by an enthalpy change only. (B) The reaction is unfavorable and driven by an entropy change only. (C) The reaction is favorable and driven by both enthalpy and entropy changes. (D) The reaction is unfavorable due to both enthalpy and entropy changes.

A (The reaction is favorable and driven by an enthalpy change only.)

NH3(g) + 2CH4(g) + 5/2O2(g) → H2NCH2COOH(s) + 3H2O(l) For the above reaction, the sign of ΔS is likely to be a) negative b) positive c) equal to zero

A (negative)

When 0.500 mol of NH3 is reacted with excess HCl, 7.00 kJ of energy is released as heat. What is ΔH for this reaction per mole of NH3 consumed? A) -3.50 kJ B) +3.50 kJ C) -14.0 kJ D) +14.0 kJ

C (-14.0 kJ)

Consider the following processes: ΔH (kJ/mol) (1/2)A → B 150. kJ/mol 3B → 2C + D -125. kJ/mol E + A → D 350. kJ/mol Calculate ΔH for: B + D → E + 2C a) 325 kJ/mol b) 525 kJ/mol c) -175 kJ/mol d) -325 kJ/mol

C (-175 kJ/mol)

Choose the correct equation for the standard enthalpy of formation of CO(g), where ΔH°f for CO = -110.5 kJ/mol (gr indicates graphite). a) 2C(gr) + O2(g) → 2CO(g), ΔH° = -110.5 kJ b) C(gr) + O(g) → CO(g), ΔH° = -110.5 kJ c) C(gr) + (1/2)O2(g) → CO(g), ΔH° = -110.5 kJ d) C(gr) + CO2(g) → 2CO(g), ΔH° = -110.5 kJ

C (C(gr) + (1/2)O2(g) → CO(g), ΔH° = -110.5 kJ)

Which of the following does not have a standard enthalpy of formation equal to zero at 25°C and 1.0 atm? a) F2(g) b) Al(s) c) H2O(l) d) H2(g)

C (H2O)

K(s) + 1/2 Cl2(g --> KCl(s) ∆H° = −437 kJ/molrxn What remains in the reaction vessel after equal masses of K(s) and Cl2(g) have reacted until either one or both of the reactants have been completely consumed? (A) KCl only (B) KCl and K only (C) KCl and Cl2 only (D) KCl, K, and Cl2

C (KCl and Cl2 only)

CH4(g) + 2 O2(g) g CO2(g) + 2 H2O(l) ΔH= 889.1 kJ ΔHf° H2O(l) = 285.8 kJ / mole ΔHf° CO2(g) = 393.3 kJ / mole What is the standard heat of formation of methane, ΔHf°CH4(g), as calculated from the data above? A) -285.8 + -393.3 + 889.1 kJ/mole B) [-285.8 + 2(-393.3)] + 889.1 kJ/mole C) [2(-285.5) + -393.3] + 889.1 kJ/mole D 889.1 - [2(-285.8) + -393.3] kJ/mole

C ([2(-285.5) + -393.3] + 889.1 kJ/mole)

For which process is ΔS negative? A) evaporation of 1 mol of CCl4(l) B) mixing 5 mL ethanol with 25 mL water C) compressing 1 mol Ne at constant temperature from 0.5 atm to 1.5 atm D) grinding a large crystal of KCl to powder

C (compressing 1 mol Ne at constant temperature from .5 to 1.5 atm)

For the following reaction CO2(g) + 2H2O(g)→CH4(g) + 2O2(g) ΔH° = 803 kJ Which of the following will increase K? A) decrease number of moles of methane B) increase volume of system C) increase the temperature of system D) A, B, and C

C (increase the temperature of system)

If 5.0 kJ of energy is added to a 10.0-g sample of water at 10.°C, the water is? A) boiling B) completely vaporized C) still a liquid D) frozen solid

C (still a liquid)

K(s) → K(g) v K(g) → K+(g) + e− w Cl2(g) → 2 Cl(g) x Cl(g) + e− → Cl−(g) y K+(g) + Cl−(g) → KCl(s) z Cl2 (g) + 2 e- → 2 Cl-(g) K(s) + 1/2 Cl2(g) → KCl (s) ΔH° = -437 kJ/mol Which of the following expressions is equivalent to the ΔH° for the reaction represented above? (A) x + y (B) x - y (C) x + 2y (D) (x/2)- y

C (x + 2y)

Consider the freezing of liquid water at -10°C and 1 atm. For this process what are the signs for ΔH, ΔS, and ΔG? ΔH ΔS ΔG A) + - 0 B) - + 0 C) - + - D) + - - E) - - -

E (- - -)

K(s) → K(g) v K(g) → K+(g) + e− w Cl2(g) → 2 Cl(g) x Cl(g) + e− → Cl−(g) y K+(g) + Cl−(g) → KCl(s) z Which of the values of ∆H° for a process in the table is less than zero (exothermic process)?

Z (K+(g) + Cl−(g) → KCl(s))

The entropy of a system decreases with an _____ in pressure.

increase

If ΔG is ___, the reaction is favored.

negative

If ΔS is ___, then the reaction is getting more organized.

negative

If ΔG is ___, the reaction is unfavorable.

positive

If ΔS is ___, then the reaction is getting less organized.

positive