Home Chapter 5 Problem Solving Center Practice Exercises

# Practice Exercises

This activity contains 28 questions.

## Which of the following is true if work has been performed on the system? Online Text

 an object is stationary no force is exerted the energy of the system must increase the energy of the system must decrease none of these

## 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?Online Text

 4.78 x 10-21 J 2.88 x 103 J 5.76 x 103 J 1.80 x 105 J 2.88 x 106 J

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

 1 erg 100 ergs 1x104 ergs 1x105 ergs 1x107 ergs

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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 10.0 kJ, exothermic 10.0 kJ, endothermic -10.0 kJ, exothermic -10.0 kJ, endothermic

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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 i and ii only i and iii only i and iv only ii and iii only ii and iv only iii and iv only

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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 126 kJ 251 kJ 502 kJ 3.26x103 kJ 6.53x103 kJ

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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 5.18 kJ -5.18 kJ 22.5 kJ -22.5 kJ

## 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? Online Text

 2.5x10-2 kJ 1.4 kJ 4.2 kJ 25 kJ

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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 dimethylhydrazine methanol ethanol octane ethylene glycol

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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 -316 kJ/mol 316 kJ/mol -632 kJ/mol 632 kJ/mol

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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 26.7 kJ/mol -26.7 kJ/mol -178 kJ/mol 178 kJ/mol -632 kJ/mol 632 kJ/mol

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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 -210.3 kJ 210.3 kJ -1264 kJ 1264 kJ +2133 kJ -999.8 kJ

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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 -234 kJ/mol -628 kJ/mol -826 kJ/mol -1220 kJ/mol -1812 kJ/mol

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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 -3.93 kJ/mol -61.2 kJ/mol -260. kJ/mol -1.10 x 103 kJ/mol -3.14 x 103 kJ/mol -8.90 x 103 kJ/mol

## What is the kinetic energy in J and cal of a 45-g golf ball moving at 61 m/s?Online Text

 168 J, 40 cal 84 J, 20 cal 84 J, 350 cal 84 kJ, 20 kcal 2.75 J, 0.67 cal

## 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?Online Text

 5.12 x 10-21 J 1.54 x 104 J 3.09 x 103 J 1.85 x 105 J 3.09 x 10-3 J

## 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?Online Text

 454 454 x 1.8 = 817 454 x 1.8 x 4.184 = 3420 454 x 4.184/1.8 = 1055 454 x 4.184 = 1900

## 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. Online Text

 500 J -140 J 140 J -500 J

## 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? Online Text

 heat work enthalpy and internal energy internal energy enthalpy

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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 821.8 kJ 4600 kJ 2.0 x 102 kJ 1.0 x 102 kJ 4.0 x 102 kJ

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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 +1430 kJ -1430 kJ -2860 kJ +2860 kJ +715 kJ

## 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?Online Text

 5.08 kJ 382 kJ 0.282 kJ 21.2 kJ 5.66 kJ

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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 -123 kJ/g, -13300 kJ/mol -25.5 kJ/g, -.235 kJ/mol -25.5 kJ/g, -2750 kJ/mol -3.57 kJ/g, -385 kJ/mol -3.24 kJ/g, -350 kJ/mol

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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 -45 kJ +45 kJ -205 kJ +205 kJ -125 kJ

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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 55.6 kJ -55.6 kJ 180.8 kJ -180.8 kJ 124.2 kJ

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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 -1165 kJ -1269 kJ -2486 kJ -2382 kJ +234 kJ

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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 149.5 kJ -149.5 kJ 227.4 kJ -2901 kJ +2901 kJ

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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 78.0 kJ/gram 7.95 kJ/gram 1.26 kJ/gram 50.3 kJ/gram 121 kJ/gram