Worksheet # 5.2 ANS
1) The value of H for the reaction below is -72 kJ. __________ kJ of heat are released when
1.0 mol of HBr is formed in this reaction.
H2 (g)  Br2 (g)  2HBr(g)
A) 144
B) 72
C) 0.44
D) 36
E) -72
Answer: D
2) The value of H for the reaction below is -126 kJ. The amount of heat that is released by
the reaction of 25.0 g of Na 2O2 with water is __________ kJ.
2Na 2O2 (s)  2H2O(l)  4NaOH(s)  O2 (g)
C) 67.5
D) 80.8
E) -126
A) 20.2
B) 40.4
Answer: A
3) The value of H for the reaction below is -336 kJ. Calculate the heat (kJ) released to the
surroundings when 23.0 g of HCl is formed.
CH4 (g) 3Cl2 (g)  CHCl3 (l)  3HCl(g)
A) 177
B) 2.57 103
C) 70.7
D) 211
E) -336
Answer: C
4) The enthalpy change for the following reaction is -483.6 kJ:
2H2 (g)  O2 (g)  2H2O(g)
Therefore, the enthalpy change for the following reaction is __________ kJ:
4H2 (g)  2O2 (g)  4H2O(g)
A) -483.6
Answer: B
B) -967.2
C) 2.34 105
D) 483.6
E) 967.2
5) The value of H for the reaction below is -1107 kJ:
2Ba(s)  O2 (g)  2BaO(s)
How many kJ of heat are released when 5.75 g of BaO(s) is produced?
A) 56.9
B) 23.2
C) 20.8
D) 193
E) 96.3
Answer: C
6) The molar heat capacity of a compound with the formula C2 H 6SO is 88.0 J/mol-K. The
specific heat of this substance is __________ J/g-K.
A) 88.0
B) 1.13
C) 4.89
D) 6.88 103
E) -88.0
Answer: B
7) A sample of aluminum metal absorbs 9.86 J of heat, upon which the temperature of the
sample increases from 23.2 °C to 30.5 °C. Since the specific heat capacity of aluminum is 0.90
J/g-K, the mass of the sample is __________ g.
A) 72
B) 1.5
C) 65
D) 8.1
E) 6.6
Answer: B
8) The specific heat capacity of lead is 0.13 J/g-K. How much heat (in J) is required to raise the
temperature of 15g of lead from 22 °C to 37 °C?
A) 2.0
B) -0.13
C) 5.8 ×104
D) 298
E) 0.13
Answer: D
9) The specific heat of liquid bromine is 0.226 J/g-K. How much heat (J) is required to raise the
temperature of 10.0 mL of bromine from 25.00 °C to 27.30 °C? The density of liquid bromine:
3.12 g/mL.
A) 5.20
B) 16.2
C) 300
D) 32.4
E) 10.4
Answer: B
10) Which one of the following statements is true?
A) Enthalpy is an intensive property.
B) The enthalpy change for a reaction is independent of the state of the reactants and products.
C) Enthalpy is a state function.
D) H is the value of q measured under conditions of constant volume.
E) The enthalpy change of a reaction is the reciprocal of the ΔH of the reverse reaction.
Answer: C
11) Which of the following statements is false?
A) Internal energy is a state function.
B) Enthalpy is an intensive property.
C) The enthalpy change for a reaction is equal in magnitude, but opposite in sign, to the enthalpy
change for the reverse reaction.
D) The enthalpy change for a reaction depends on the state of the reactants and products.
E) The enthalpy of a reaction is equal to the heat of the reaction.
Answer: B
12) A chemical reaction that absorbs heat from the surroundings is said to be __________ and
has a __________ ΔH at constant pressure.
A) endothermic, positive
B) endothermic, negative
C) exothermic, negative
D) exothermic, positive
E) exothermic, neutral
Answer: A
13) The reaction
ΔH° = -3351 kJ
4Al(s)  3O2 (g)  2Al2O3 (s)
is __________, and therefore heat is __________ by the reaction.
A) endothermic, released
B) endothermic, absorbed
C) exothermic, released
D) exothermic, absorbed
E) thermoneutral, neither released nor absorbed
Answer: C
14) Under what condition(s) is the enthalpy change of a process equal to the amount of heat
transferred into or out of the system?
(a) temperature is constant
(b) pressure is constant
(c) volume is constant
A) a only
B) b only
C) c only
D) a and b
E) b and c
Answer: B
15) The units of of heat capacity are __________.
A) K/J or °C/J
B) J/K or J/ °C C) J/g-K or J/g- °C D) J/mol
Answer: B
E) g-K/J or g- °C/J
16) An 8.29 g sample of calcium carbonate CaCO3 (s) absorbs 50.3 J of heat, upon which the
temperature of the sample increases from 21.1 °C to 28.5 °C. What is the specific heat of
calcium carbonate?
A) .63
B) .82
C) 1.1
D) 2.2
E) 4.2
Answer: B
AP Practice
2002 D Required
Answer:
(a) q in J, m in grams, C in J/g˚C, T in ˚C
(b) mass or volume of each solution
starting temperature of each reagent
ending temperature of mixture
(c) (i) both are 1 M acid and base and react on a 1:1 basis
1 mol HCl
1 mol H+
volume  1000 mL  1 mol HCl = mol of H+
H+ + OH–  H2O
joules released
(ii) mol H O produced
2
(d) (i) increases. Twice as much water is produced so it is twice the energy released in the same
volume of solution
twice energy
(ii) same. twice mol water = same result
(e) smaller. heat lost to the air gives a smaller amount of temperature change in the solution,
which leads to a smaller measured heat release