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Practice Exercises



This activity contains 28 questions.

Question 1.
Which of the following is true if work has been performed on the system?

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Question 2.
At 0°C the average velocity of CH4 molecules in air is 600. m/s. What is the total kinetic energy of 1.00 mol of CH4 molecules moving at this speed?

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Question 3.
A common unit of energy is the erg, 1 g cm2/s2. How many ergs are there in 1 J?

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Question 4.

Calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic for a chemical reaction in which 10.0 kJ of heat is absorbed while the system does no work on the surroundings.

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Question 5.

For a process in which the internal energy does not change, which of the following are possible?

(i) heat > 0, work < 0

(ii) heat > 0, work > 0

(iii) heat < 0, work < 0

(iv) heat < 0, work > 0

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Question 6.

Consider the following reaction:

2C2H2(g) + 5O2(g) --> 4CO2(g) + 2H2O(g) H = -2511 kJ/mol

Calculate the amount of heat transferred when 2.60 g of C2H2(g) is consumed in this reaction at constant pressure.

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Question 7.

Consider the reaction

Pb2+(aq) + 2Cl-(aq) --> PbCl2(s) H = -22.53 kJ/mol

Calculate H when 0.230 mol of PbCl2(s) is dissolved in water.

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Question 8.
How many kJ of heat must be removed from 1000. g of water (heat capacity of 4.184 J g-1 K-1) to lower the temperature from 18.0°C to 12.0°C?

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Question 9.

The fuel used in spacecrafts must contain as much energy per gram of material as possible. Based on this consideration only, which of the following fuels is best suited to be a spacecraft fuel?

(i) dimethylhydrazine, (CH3)2NNH2 Hcombustion = -1694 kJ/mol

(ii) methanol, CH3OH Hcombustion = -726 kJ/mol

(iii) ethanol, C2H5OH Hcombustion = -1371 kJ/mol

(iv) octane, C8H18 Hcombustion = -5500 kJ/mol

(v) ethylene glycol, C2H6O2 Hcombustion = -1190 kJ/mol

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Question 10.

From the following heats of reaction,

2C (graphite) + 2H2 (g) + O2 (g) --> 2H2CO (g) H = -217 kJ/mol

2C (graphite) + 2H2 (g) + 2O2 (g) --> 2H2CO2 (l) H = -849 kJ/mol,

calculate the heat for the reaction

2H2CO (g) + O2 (g) --> 2H2CO2 (l)

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Question 11.

From the following heats of reaction,

2C (graphite) + H2 (g) --> C2H2 (g) H = 227 kJ/mol

6C (graphite) + 3H2 (g) --> C6H6 (l) H = 49 kJ/mol

calculate the heat for the reaction

3C2H2 (g) --> C6H6 (l)

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Question 12.

The heat of combustion of fructose, C6H12O6, is -2812 kJ/mol. Using the information in Table 5.3, calculate f for fructose.

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Question 13.

Calculate the standard enthalpy of formation of solid SrCO3, given the following data:

2Sr (s) + O2 (g) --> 2SrO (s) H = -1184 kJ/mol

SrO (s) + CO2 (g) --> SrCO3 (s) H = -234 kJ/mol

C (graphite) + O2 (g) --> CO2 (g) H = -394 kJ/mol

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Question 14.

A 2.839-g sample of C2H4O was burned in a bomb calorimeter whose total heat capacity is 16.77 kJ/°C. The temperature of the calorimeter increases from 22.62°C to 26.87°C. What is the heat of combustion per mole of C2H4O?

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Question 15.
What is the kinetic energy in J and cal of a 45-g golf ball moving at 61 m/s?

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Question 16.
At 20°C (approximately room temperature) the average velocity of F2 molecules in air is 902 mi/hr. What is the total kinetic energy of 1 mol of F2 molecules moving at this speed?

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Question 17.
In much engineering work it is common to use the British thermal unit (Btu). A Btu is the amount of heat required to raise the temperature of 1 lb of water by 1°F. What is the number of J in a Btu?

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Question 18.
Calculate the change in internal energy of the system for the following process:

A balloon is heated by adding 320 J of heat. It expands, doing 180 J of work on the atmosphere.

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Question 19.
Which of the following quantities -- heat, work, enthalpy, internal energy -- depend only on the end points and not on the path followed in a process?

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Question 20.

Consider the following reaction:

2Na(s) + Cl2(g) --> 2NaCl(s) H = -821.8 kJ

What is the amount of heat transferred when 5.6 g of Na(s) reacts at constant pressure?

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Question 21.

Consider the combustion reaction of ethane gas, C2H6(g):

C2H6(g) + 7/2O2(g) --> 2CO2(g) + 3H2O(g) H = -1430 kJ

What is the enthalpy change for the reverse reaction if whole-number coefficients are used?

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Question 22.
How much heat is needed to raise the temperature of 75.2 mol of water (heat capacity of 4.184 J g-1 K-1) from 12.5°C to 80.0°C?

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Question 23.

A 2.20-g sample of quinone, C6H4O2, is burned in a bomb calorimeter whose total heat capacity is 7.854 kJ/°C. The temperature of the calorimeter increases from 23.44°C to 30.57°C. What is the heat of combustion per gram of quinone? Per mole of quinone? (Molecular weight of quinone is 108.1.)

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Question 24.

Suppose you are given the following hypothetical reactions:

X --> Y H = -80 kJ

X --> Z H = -125 kJ

Use Hess's law to calculate the enthalpy change for the reaction Y --> Z.

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Question 25.

From the following heats of reaction,

N2(g) + 2O2(g) --> 2NO2(g) H= +67.6 kJ

2NO(g) + O2(g) --> 2NO2(g) H= -113.2 kJ

calculate the heat of the reaction

N2(g) + O2(g) --> 2NO(g)

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Question 26.

From the following enthalpies of reaction,

H2(g) + F2(g) --> 2HF(g) H = -537 kJ

C(s) + 2F2(g) --> CF4(g) H = - 680 kJ

2C(s) + 2H2(g) --> C2H4(g) H = +52.3 kJ

calculate H for the reaction of ethylene with F2:

C2H4(g) + 6F2(g) --> 2CF4(g) + 4HF(g)

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Question 27.

Using values from Appendix C or the toolbox, calculate the standard enthalpy change for the following reaction:

Fe2O3(s) + 6 HCl(g) --> 2FeCl3 + 3H2O(g)

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Question 28.

A 1.55-g sample of propane, C3H8, was burned in a bomb calorimeter whose total heat capacity is 12.3 kJ/°C. The temperature of the calorimeter plus its contents increased from 21.36°C to 27.69°C. What is the heat of combustion per gram of octane?

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