Exam 5: Thermochemistry: Energy Changes in Reactions

Which of the following is an endothermic process for the system? In each case, the "system" is underlined.

C₈H₁₈ (114 g/mol, d  0.69 g/mL) is a good model for gasoline, and C₁₆H₃₄ (226 g/mol, d  0.85 g/mL) is a good model for diesel fuel. These compounds have enthalpies of combustion of 5,460 kJ/mol and 10,800 kJ/mol, respectively. Calculate the fuel density (kJ/mL) of these compounds, and determine how many times more valuable diesel fuel is in terms of its energy content as measured by fuel density.

You heat a cup of coffee in a microwave oven. It absorbs 40 kJ of energy from the microwave, and the volume expands. Which one of the following statements correctly describes the relationship between the change in enthalpy H and the change in internal energy E of the coffee? ( means greater than,  means less than)

The best definition of the enthalpy change is ________

If 7.3 kJ of energy are required to change the temperature of water from 5.0 to 70.0 , what was the volume of water? (c_s  4.184 J/(g  ), d  1.00 g/mL)

The capacity to do work is a definition of ________

A pot of water is heated with 10 J of energy at constant pressure. What is the enthalpy change (H) for this process?

Determine the enthalpy of formation for glucose (C₆H₁₂O₆) given the following enthalpies of formation (CO₂(g), 393.5 kJ/mol; H₂O(l), 285.8 kJ/mol) and the enthalpy for the reaction shown below. C₆H₁₂O₆(s) 6O₂ (g) 6CO₂(g) 6H₂O(l) H 2801 kJ

Use the following information to determine the enthalpy for the reaction shown below. CS₂(l) 3O₂(g) CO₂(g) 2SO₂(g) H^o  ? C(graphite) O₂(g) CO₂(g) H^o  393.5 kJ S(s) O₂(g) SO₂(g) H^o  296.8 kJ C(graphite) 2S(s) CS₂(l) H^o  87.9 kJ

In an experiment, 7.5 g of liquid water at 35 is converted into steam with a temperature of 145C. How much energy is required for this process? _vap  2,260 J/g; H_fus  334 J/g; c_s(ice)  2.06 J/(g  ); c_s(water)  4.18 J/(g  ); c_s(steam)  1.99 J/(g  ))

Describe the difference between potential energy and kinetic energy, and give an example of each.

Motor fuels are mixtures of hydrocarbons, but they can be characterized by their average properties. Gasoline (114 g/mol average, d  0.69 g/mL) and diesel fuel (226 g/mol average, d  0.85 g/mL) have average enthalpies of combustion of 5,650 kJ/mol and 10,200 kJ/mol, respectively. Calculate the fuel density (kJ/mL) of these compounds, and determine how many times more valuable diesel fuel is in terms of its energy content as measured by fuel density.

Which statement regarding combustion of a sample of gasoline in a bomb calorimeter is correct?

The basal metabolic rate (BMR) is the minimum energy intake required to maintain a body that is awake and at rest. Although the rate varies with age, gender, health, and body mass, a reasonable value is 1,600 Cal per day. Walking can require 2.5 times the BMR, and exertion in work or sports can require 7 times the BMR. Using this information, calculate the energy expended by someone walking at a speed of 3.0 mph and determine how far she could walk with the energy from a quarter-pound hamburger (125 g) that has a food value of 3.6 Cal/g.

The energy content of a Big Mac is 540 Cal. How much water can be heated from 20 to 90 by this amount of energy? (c_P(water)  1.00 g/mL, c_s(water)  4.18 J/(g  ), 1 Cal  1,000 cal  4.184 kJ)

During an exothermic process, ________ for the system.

Work is done when a force moves an object some distance. Newton defined force as mass times acceleration. Acceleration is the rate at which velocity changes. What are the units of work?

Which statement below regarding the various heat capacities is not correct?

What is the change in internal energy (E) of a system when it loses 10 kJ of energy and 5,000 J of work is done on the system?

Given the following thermochemical equation detailing the combustion of methane CH₄(g) 2O₂(g) CO₂(g) 2H₂O(g) H_rxn  802 kJ/mol CH₄ determine the amount of energy released when 25 g of methane undergoes combustion.