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Homework #9 Chapter 9
Name ________________ Student ID ______________ Date ______________
1
How fast (in meters per second) must an iron ball with a mass of 56.6 g be
traveling in order to have a kinetic energy of 15.75 J?
2
How many kilojoules are equal to 3.27 L atm of work?
3
Calculate (a) q when a system does 54 J of work and its energy decreases by 72 J
and (b) E for a gas that releases 38 J of heat and has 102 J of work done on it.
4
In which case is heat added to the system: (a) ∆E = –43 J, w = 40 J; or (b) ∆E =
31 J, w = 34 J?
5
The material typically used to heat metal radiators is water. If a boiler generates
water at 79.5°C, what mass of water was needed to provide the heat of 350,000
J? Water has a specific heat of 4.184 J g–1 °C–1 and room temperature is 25 °C.
6
How does the specific heat of water explain why cities on the coast of large
bodies of water tend to be cooler in the summer than cities several miles inland?
7
Why is enthalpy generally more useful than internal energy in the
thermodynamics of real world systems?
8
List at least two phase changes that are exothermic processes.
9
The heat of fusion of pure silicon is 43.4 kJ/mol. How much energy would be
needed to melt a 5.24-g sample of silicon at its melting point of 1693 K?
10
Calculate the energy required to convert 1.70 g of ice originally at –12.0°C into
steam at 105°C.
11
When a 13.0-g sample of NaOH(s) dissolves in 400.0 mL water in a coffee cup
calorimeter, the temperature of the water changes from 22.6°C to 30.7°C.
Assuming that the specific heat capacity of the solution is the same as for water,
calculate (a) the heat transfer from system to surroundings and (b) H for the
reaction
12
NaOH(s) → Na+(aq) + OH–(aq)
Write the formation reaction for each of the following substances: (a) CH4 (g);
(b) C3H8 (); (c) HCl (g); (d) C6H12O6 (s); (e) NaF (s).
13
Which of the following are state functions? (a) the volume of a balloon, (b) the
time it takes to drive from your home to your college or university, (c) the
temperature of the water in a coffee cup, (d) the potential energy of a ball held in
your hand.
14
The phase change between graphite and diamond is difficult to observe directly.
Both substances can be burned, however. From these equations, calculate ∆H°
for the conversion of diamond into graphite:
15
C(s, graphite) + O2(g) → CO2(g)
∆H° = –393.51 kJ
C(s, diamond) + O2(g) → CO2(g)
∆H° = –395.94 kJ
Using heats of formation tabulated in Appendix E, calculate the heats of reaction
for the following.
(a) C2H2(g) +
5
O2(g) → 2 CO2(g) + H2O()
2
(b) PCl3(g) + Cl2(g) → PCl5(g)
(c) C2H4(g) + H2O(g) → C2H5OH(g)
(d) Fe2O3(s) + 2 Al(s) → Al2O3(s) + 2 Fe()
*The aluminum oxide and iron
produced in the reaction are assumed to have cooled to solid states.
16
Nitroglycerine, C3H5(NO3)3(), is an explosive most often used
in mine or quarry blasting. It is a powerful explosive because four
gases (N2, O2, CO2, and steam) are formed when nitroglycerine is
detonated. In addition, 6.26 kJ of heat is given off per gram of
nitroglycerine detonated. (a) Write a balanced thermochemical
equation for the reaction. (b) What is H when 4.65 mol of products
is formed?
17
Sulfur trioxide can be removed from the exhaust gases of power plants by
reaction with lime according to the equation, CaO(s) + SO3(g) → CaSO4(s), with
∆H° = –886 kJ. If 240 kg of SO3 is to be removed, how much heat is released?
18
Most first aid “cold packs” are based on the endothermic dissolution of
ammonium nitrate in water:
NH4NO3(s) → NH4+(aq) + NO3–(aq)
H = 25.69 kJ
A particular cold pack contains 50.0 g of NH4NO3 and 125.0 g of water. When
the pack is squeezed, the NH4NO3 dissolves in the water. If the pack and its
contents are initially at 24.0C, what is the lowest temperature that this bag could
reach? (Assume that the ammonium nitrate solution has a specific heat of 4.25 J
g–1 K–1, and that the heat capacity of the bag itself is small enough to be
neglected. Colligative properties of the solution lower the freezing point to –18°C
which means that the solution will not freeze at a temperature above –18°C.
19
Hydrogen combines with oxygen in fuel cells according to the thermochemical
equation
2H2(g) + O2(g) → 2 H2O(g)
∆H° = –571.7 kJ
Suppose that you are working with a firm that is using hydrogen fuel cells to
power satellites. The satellite requires 4.0  105 kJ of energy during its useful
lifetime to stabilize its orbit. How many grams of hydrogen is need for the fuel
cell?
20
Suppose there is 2.43 mol of nitrogen gas in an insulated, sealed 31.7-L container
initially at 285 K. The specific heat of nitrogen gas is 1.04 kJ kg-1 K-1 (note
units). If a 5.44-kg block of iron (specific 0.444 J g-1 K-1) at 755 K is placed in
this container and it is sealed again (with no loss of nitrogen and neglect the
volume of the iron), what is the final pressure of the nitrogen gas?

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