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© 2014 Pearson Education, Inc. Chemistry: A Molecular Approach, 3rd Edition Nivaldo J. Tro

For Practice 6.1 A cylinder and piston assembly (defined as the system) is warmed by an external flame. The contents of the cylinder expand, doing work on the surroundings by pushing the piston outward against the external pressure. If the system absorbs 559 J of heat and does 488 J of work during the expansion, what is the value of E?

Internal Energy, Heat, and Work


For Practice 6.2 To determine whether a shiny gold-colored rock is actually gold, a chemistry student decides to measure its heat capacity. She first weighs the rock and finds it has a mass of 4.7 g. She then finds that upon absorption of 57.2 J of heat, the temperature of the rock rises from 25 °C to 57 °C. Find the specific heat capacity of the substance composing the rock and determine whether the value is consistent with the rock being pure gold. For More Practice 6.2 A 55.0 g aluminum block initially at 27.5 °C absorbs 725 J of heat. What is the final temperature of the aluminum?

Temperature Changes and Heat Capacity


For Practice 6.3 A block of copper of unknown mass has an initial temperature of 65.4 °C. The copper is immersed in a beaker containing 95.7 g of water at 22.7 °C. When the two substances reach thermal equilibrium, the final temperature is 24.2 °C. What is the mass of the copper block?

Thermal Energy Transfer


For Practice 6.4 A cylinder equipped with a piston expands against an external pressure of 1.58 atm. If the initial volume is 0.485 L and the final volume is 1.245 L, how much work (in J) is done? For More Practice 6.4 When fuel is burned in a cylinder equipped with a piston, the volume expands from 0.255 L to 1.45 L against an external pressure of 1.02 atm. In addition, 875 J is emitted as heat. What is ΔE for the burning of the fuel?

Pressure–Volume Work


For Practice 6.5 When 1.550 g of liquid hexane (C6H14) undergoes combustion in a bomb calorimeter, the temperature rises from 25.87 °C to 38.13 °C. Find ΔErxn for the reaction in kJ/mol hexane. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.73 kJ/ °C. For More Practice 6.5 The combustion of toluene has a ΔErxn of –3.91 × 103 kJ/mol. When 1.55 g of toluene (C7H8) undergoes combustion in a bomb calorimeter, the temperature rises from 23.12 °C to 37.57 °C. Find the heat capacity of the bomb calorimeter.

Measuring ΔErxn in a Bomb Calorimeter


For Practice 6.6 Identify each process as endothermic or exothermic and indicate the sign of ΔH. a. an ice cube melting b. nail polish remover quickly evaporating after it is accidentally spilled on the skin c. gasoline burning within the cylinder of an automobile engine

Exothermic and Endothermic Processes


For Practice 6.7 Ammonia reacts with oxygen according to the equation: Calculate the heat (in kJ) associated with the complete reaction of 155 g of NH3.

Stoichiometry Involving ΔH


For More Practice 6.7 What mass of butane in grams is necessary to produce 1.5 × 103 kJ of heat? What mass of CO2 is produced?

Stoichiometry Involving ΔH


Measuring ΔHrxn in a Coffee-Cup Calorimeter For Practice 6.8 The addition of hydrochloric acid to a silver nitrate solution precipitates silver chloride according to the reaction: When 50.0 mL of 0.100 M AgNO3 is combined with 50.0 mL of 0.100 M HCl in a coffee-cup calorimeter, the temperature changes from 23.40 °C to 24.21 °C. Calculate ΔHrxn for the reaction as written. Use 1.00 g/mL as the density of the solution and C = 4.18 J/g · °C as the specific heat capacity.


For Practice 6.9 Find ΔHrxn for the reaction: Use these reactions with known ΔH’s:

Hess’s Law


For More Practice 6.9 Find ΔHrxn for the reaction: Use these reactions with known ΔH’s:

Hess’s Law


For Practice 6.10 Write equations for the formation of (a) NaCl(s) and (b) Pb(NO3)2(s) from their respective elements in their standard states. Include the value of for each equation.

Standard Enthalpies of Formation


For Practice 6.11 The thermite reaction, in which powdered aluminum reacts with iron oxide, is highly exothermic. Use standard enthalpies of formation to find for the thermite reaction.

The reaction of powdered aluminum with iron oxide, known as the thermite reaction, releases a large amount of heat.

and Standard Enthalpies of Formation


For Practice 6.12 The chemical hand warmers described in Section 6.1 produce heat when they are removed from their airtight plastic wrappers. Recall that they utilize the oxidation of iron to form iron oxide according to the reaction . Calculate for this reaction and calculate how much heat is produced from a hand warmer containing 15.0 g of iron powder.

and Standard Enthalpies of Formation


For Practice 6.13 What mass of CO2 (in kg) does the combustion of a 15-gallon tank of gasoline release into the atmosphere? Assume the gasoline is pure octane (C8H18) and that it has a density of 0.70 g/mL.

Fossil Fuels and Climate Change

internal energy, heat, and work · pdf fileinternal energy, heat, and work . ... she first...

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