Exam 5: Thermochemistry: Energy Changes in Reactions

Ethanol is being promoted as renewable biofuel. Use the standard enthalpies of formation below to determine the standard enthalpy of combustion of ethanol. Substance \circ in kJ/mol (l) -277 (g) -394 (l) -286

Complete the table below, and identify the fuel with the highest fuel density. Substance Model Compound Molar Mass (/) Enthalpy of Combustion (/) Density (/) Fuel Density (/) Heating oil 226.0 10,800 0.85 Coal 1,906 44,000 1.40 Wood 180.0 2,540 0.50

The destruction of the ozone layer by chlorofluorocarbons can be described by the following reactions, all occurring in the gas phase. +\rightarrow+2 \Delta=-29.90 2\rightarrow3 \Delta= +\rightarrow+ \Delta=54.08 What is $\Delta$ H°_rxn for the decomposition of ozone to oxygen?

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.

What is the kinetic energy of a skier weighing 175 lb traveling 60 mph? (2.205 lb = 1 kg, 1 mi = 1.609 km, 1 J = 1 kg m²s^-2)

Assume gasoline has an energy density of 129 MJ/gal, and diesel fuel has an energy density of 145 MJ/gal. If gasoline costs $3.00 per gallon, how much should a gallon of diesel fuel cost so they have the same economic value (MJ/$)?

Isooctane is a good model compound for gasoline. When 1.14 g of isooctane (C₈H₁₈, molar mass = 114 g/mol) reacted with excess oxygen in a constant volume calorimeter, the temperature of the calorimeter increased by 5.83°C. The calorimeter consisted of two components: a steel vessel with a heat capacity of 1.00 kJ/ °C and 2.00 L of water surrounding it. The density and specific heat capacity of water are 1.00 g/mL and 4.184 J/(g . °C), respectively. Use these data to determine the molar enthalpy of combustion of isooctane.

Assuming that the distances between the two ions are the same in all cases, which of the following ion pairs has the greatest electrostatic potential energy (i.e., largest in magnitude)?

There is concern that the combustion of fossil fuels such as coal and petroleum contributes to climate change by adding carbon dioxide to the atmosphere. Electric cars are being promoted as a way to address this situation by reducing the use of gasoline. Yet most electricity is produced by coal-fired power plants. Several factors need to be considered in determining whether electric cars actually are helpful in this regard. One is the environmental value of these fuels. Estimate the environmental value of coal compared to gasoline from the following information. The environmental value is defined as the amount of energy obtained per mole of carbon dioxide produced, so a larger environmental value is better. Substance Model Compound Molar Mass combution coal 1,906/ 44,000/ gasoline 114/ 5,460/

In an experiment, 30.0 g of metal was heated to 98.0°C and then quickly transferred to 50.0 g of water in a calorimeter. The heat capacity of the calorimeter with the water was 211 J/°C. The initial temperature of the calorimeter was 27.0°C, and the final temperature after addition of the metal was 32.5°C. What is the value of the specific heat capacity of the metal?

How much energy is needed to change the temperature of 25.00 mL of water from 10.0°C to 95.0°C? (c_s = 4.184 J/(g . °C), d = 1.00 g/mL)

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.

Ethanol (CH₃CH₂OH) has been suggested as an alternative fuel source. Ethanol's enthalpy of combustion is $\Delta$ H_comb = -1,368 kJ/mol. What volume of ethanol (d = 0.789 g/mL) is required to produce the same amount of energy as 1 gallon of gasoline, which can be modeled as isooctane (C₈H₁₈) with an energy density of 32.9 kJ/mL? (1 gal = 3.785 L; d = 0.703 g/mL)

When a 13.0 g sample of NaOH(s) dissolves in 400.0 mL of water to produce 413.0 g of solution in a constant pressure calorimeter, the temperature of the water and reaction vessel changes from 22.6°C to 30.6°C. Assume that the specific heat capacity of the solution is 4.20 J/(g . °C), and that the heat capacity of the reaction vessel is 1.00 J/°C. What is the molar enthalpy of solution of sodium hydroxide (40.00 g/mol)?

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

In terms of the enthalpy of formation, which of the following compounds is most stable relative to its elements under standard conditions?

During a(n) ________ process, energy is transferred to the system from the surroundings.

What will be the final temperature of a 10.0 g piece of iron (C_P = 25.09 J/(mol · °C)) initially at 25°C, if it is supplied with 9.5 J from a stove?

In a Reuters news report dated February 3, 2010, President Obama is quoted as saying, "By 2022 we will more than double the amount of biofuels we produce to 36 billion gallons, which will decrease our dependence on foreign oil by hundreds of millions of barrels per year." Use the following information to estimate the fraction of farmland in the United States that will be needed to meet this target in order to assess the impact on other uses of farmland, such as the production of food. (M = mega = 10⁶) Farmland in the U.S. = 1.4 *10⁶ square miles Energy density of biofuels = 100 MJ/gal Annual biofuel production from farmland = 1,000 gal/acre 640 acres = 1 square mile 1 gal = 3.785 L Mass density of biofuels: 800 g/L

Work requires ________