Download Practice ws on Ch 5 - mvhs

Chapter 5 Problems
1. How many joules must be added to a 63.43-g sample of Fe(s) to raise the
sample’s temperature from 19.7 to 54.2° C? Assume that the specific heat of iron
is constant over this temperature range.
Answer: 9.8 x 10^2 J
2. How many joules must be added to a 7.92-g sample of CH3CH2OH(l) to raise the
sample’s temperature from 6.8 to 75.2 ° C?
Answer: 1.31 x 10^3 J
3. How many joules must be removed from a 287-g sample of CH3CH2OH(l) to
lower the sample’s temperature from 56.2 to 19.8 ° C?
Answer: 2.53 x 10^4 J
4. A 1.00 M aqueous solution of NaOH, a 0.50 M aqueous solution of H2SO4, and a
coffee-cup calorimeter were allowed to stand at a room temperature of 25.4 °C
until the temperature of all three reached 25.4 C. A 50.0-mL sample of the 1.00 M
NaOH was then placed in the calorimeter. 50.0 mL if the 0.50 M H2SO4 was
added as rapidly as possible and the two solutions were mixed thoroughly, the
temperature rose to 31.9° C. From this experiment, what is the heat of
neutralization of one mole of H2SO4? For simplicity, assume that the densities of
the NaOH and H2SO4 solutions were 1.00 g/mL and that the specific heat of the
solution after reaction was 4.18 J/g °C.
Answer: -112 kJ/mol
5. A 1.00 M solution of NaOH, a 1.00 M solution of HCl, and a calorimeter were
allowed to stand at a room temperature of 19.5°C until the temperature of all three
reached 19.5°C. A 200.0-mL sample of the 1.00 M NaOH was then placed in the
calorimeter, 200.0 mL of the 1.00 M HCl was added as rapidly as possible, and
the two solutions were mixed thoroughly.The temperature rose to 25.8°C.
a) From this experiment, what is the heat of neutralization of one mole of
HCl? Assume densities of NaOH and HCl solutions were 1.00 g/mL and
that the specific heat of solution after reaction was 4.18 J/g°C.
b) Compare the heat of neutralization of one mole of HCl with the heat of
neutralization of one mole of sulfuric acid in Problem 4 and explain the
difference.
Answer: a) –53 kJ/mol b) molar heat of neutralization HCl = ½(molar heat of
neutralization H2SO4)
6. For the burning of methane gas, CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)
Heat of rxn = -890.32 kJ. How many kilojoules will be given off by the burning
of 451 g of methane?
Answer: 2.51 x 10^4 kJ
7. For burning of isooctane, 2 (CH3)2CHCH2C(CH3)3 (l) + 25O2(g) -> 16CO2(g) +
18H2 (l). Heat of rxn = -10930.9 kJ. How many kilojoules will be given off by the
burning of 369 g of isooctane?
Answer: 1.77 x 10^4 kJ
8. Calculate deltaH(rxn) for the reaction 2Ca(s) + 2C(graphite) + 3O2(g) ->
2CaCO3(s) from the following information:
2Ca(s) + O2(g) -> 2CaO(s) ΔH = -1270.18 kJ
C(graphite) + O2(g) -> CO2(g) ΔH = -393.51 kJ
CaO(s) + CO2(g) -> CaCO3(s) ΔH = -178.32 kJ
Answer: -2413.84 kJ
9. Given the thermochemical equation 2Hg(l) + O2(g) -> 2HgO(s) deltaH = -181.66
kJ
a) Write the thermochemical equation for the decomposition of 2 mol
HgO(s) to Hg(l) and O2(g).
b) Write the thermochemical equation that shows the formation of 1 mol
HgO from Hg(l) and O2(g).
Answer: a) 2HgO(s) -> 2Hg(l) + O2(g) ΔH = +181.66 kJ
b) Hg(l) + 1/2O2(g) ->HgO(s) ΔH = -90.83 kJ