AP CHEMISTRY Thermochemistry STUDY GUIDE
Due – Wednesday
1)What is the specific heat, c, (J·g-1·K-1) of a substance if650 J of heat are required to raise the temperature of 1.5grams of this substance from 10.5 ºC to 25.5 ºC?
2)In a calorimetry experiment, the temperature of 500mL of water rose from 19.78 ºC to 28.65 ºC when 2.0 g ofsodium metal reacted according to the following balancedequation. 2 Na (s) + H2O (l) →2 NaOH (aq) + H2 (g)Using the assumption that the calorimeter’s heat capacityis due only to the 500 grams of water (specific heat =4.184 J/(g K)), calculate qrxn, and ΔHrxn (in kJ) for thereaction as written.
3)Consider that the following enthalpy changes areknown for the statedreactions 1-3 below. Using Hess’Law, calculate the enthalpy change for reaction #4?
1. N2 (g) + 2 H2 (g) → N2H4 (l) ΔH1 = +50.6 kJ
2. H2 (g) + O2 (g) → H2O2 (l) ΔH2 = -187.8 kJ
3. 2 H2 (g) + O2 (g) → 2 H2O (g) ΔH3 = -483.6 kJ
4. N2H4 (l) + 2 H2O2 (l) → N2 (g) + 4 H2O (g)
4)Which is true if ΔH = - 95 J?
A) Both the system and the surroundings are gaining 95 J.
B) Both the system and the surroundings are losing 95 J.
C) The system is gaining 95 J, while the surroundings are losing 95 J.
D) The system is losing 95 J, while the surroundings are gaining 95 J.
E) The system is losing -95 J, while the surroundings are gaining 95 J.
5)How much energy is released during the formation of 98.7 g of Fe, according to thereaction below?
Fe2O3(s) + 2 Al(s) Al2O3(s) + 2 Fe(s) ΔH°rxn = -852 kJ
6) Use the standard reaction enthalpies given below to determine ΔH°rxn for the followingreaction:
P4(g) + 10 Cl2(g) 4PCl5(s) ΔH°rxn = ?
Given:
PCl5(s) PCl3(g) + Cl2(g) ΔH°rxn= 157 kJ
P4(g) + 6 Cl2(g) 4 PCl3(g) ΔH°rxn = -1207 kJ
7)Use the information provided to determine ΔH°rxn for the following reaction:
3 Fe2O3(s) + CO(g) 2 Fe3O4(s) + CO2(g) ΔH°rxn= ?
ΔH°f (kJ/mol)
Fe2O3(s) -824
Fe3O4(s) -1118
CO(g) -111
CO2(g) -394
8) A student is preparing to perform a series of calorimetry experiments. She first wishes todetermine the heat capacity of the calorimeter (Ccal) for her coffee cup calorimeter. Shepours a 50.0 mL sample of water at 72.0 °C into the calorimeter containing a 50.0 mLsample of water at 25.0 °C. She carefully records the final temperature of the water as 44.0°C. What is the value of Ccal for the calorimeter?
9) What is the molar mass of a metal predicted by the Dulong-Petit law if the metal has aspecific heat capacity of 0.128 J/g°C?
10) 14.0 g of metal at 24.0 °C has 250 joules of heat added to it. The metal's specific heat is 0.105J/g °C. What is its final temperature?
11) How much work in joules is done when a piston expands from a volume of 13.27 liters to76.55 liters against a pressure of 14.89 atm?
12) Which of the following signs on q and w represent a system that is doing work on thesurroundings, as well as losing heat to the surroundings?
A) +q , +w
B) -q , -w
C) +q , -w
D) -q , +w
E) None of the above.
13)Which of the following is NOT a state property?
A) pressure
B) temperature
C) internal energy
D) enthalpy
E) work
14)How can energy be transferred to or from a system?
A) Energy can only be transferred as potential energy being converted to kinetic energy.
B) Energy can be transferred only as heat.
C) Energy can be transferred only as work.
D) Energy can be transferred as heat and/or work.
15)Which of the following is an example of a state function?
A) The length of time it takes to go from New York to Los Angeles
B) The mileage traveled going from San Francisco to Los Angeles
C) The amount of time it takes to change the channel when Gossip Girl comes on.
D) The difference in altitude between Chicago and Denver
16)A chemical reaction where heat is transferred to the surroundings is a(n) ______reaction.
17)Which of the following is an endothermic process?
A) jet fuel burning in a jet engine B) combustion of methane
C) freezing of water D) vaporization of water
18)In a refrigeration system, the refrigerant gas absorbs 21.39 kJ of energy while expandingagainst a 0.278 atmosphere pressure from a volume of 0.0423 liters to a volume of 1.876liters. What is the energy change of the gas?
19) How much work in joules is done on the system when a 1.15 atm external pressure causes a piston to decrease in volume from 6.55 liters to 3.16 liters?
20) When power was turned off to a 30.0 gal. water heater, the temperature of the waterdropped from 75.0 °C to 22.5 °C. How much heat was lost to the surroundings? (1 gal =3.785 L)
21) 14.0 g of metal at 24.0 °C has 250 joules of heat added to it. The metal's specific heat is 0.105 J/g °C. What is its final temperature?
22) Twoaqueous solutions at room temperature are mixed in a coffee cup calorimeter. The reactioncauses the temperature of the resulting solution to fall below room temperature. Which of the following statements is TRUE?
A) Energy is leaving the system during reaction.
B) The products have a lower potential energy than the reactants.
C) This type of experiment directly yields DErxn.
D) The mixing is endothermic.
E) The solution has special properties that enable it to violate the first and second law of
thermodynamics.
1