Exam 6: Thermochemistry: Energy Flow and Chemical Change

A backpacker collects snow at 0°C, and places it in a cooking pot on a camp stove. It takes 643 kJ of heat energy to melt the snow and bring the water to boiling. Assuming no heat loss, and neglecting the specific heat capacity of the pot, calculate the mass of snow that the backpacker collected. (Data: specific heat capacity of liquid water, c = 4.18 J/g·K; and: H₂O(s) → H₂O(l) ΔH = ΔH_fusion = 6.02 kJ/mol)

In which one of the following processes is ΔH = ΔE?

What is the final temperature when 20.0 g of water at 25°C is mixed with 30.0 g of water at 80°C?

Which one of the following is a correct formation reaction?

For a reaction in a sealed, rigid container, ΔH is always greater than ΔE.

A 1.00 g piece of copper metal is initially at 100.0°C. It is dropped into a coffee cup calorimeter containing 50.0 g of water at a temperature of 20.0°C. After stirring, the final temperature of both copper and water is 25.0°C. Assuming no heat losses, and that the specific heat (capacity) of water is 4.18 J/(g·K), what is the heat capacity of the copper in J/K?

For all processes, both q and w will have the same sign.

When Karl Kaveman adds chilled grog to his new granite mug, he removes 10.9 kJ of energy from the mug. If it has a mass of 625 g and was at 25°C, what is its new temperature? Specific heat capacity of granite = 0.79 J/(g·K)

Natural gas, or methane, is an important fuel. Combustion of one mole of methane releases 802.3 kilojoules of energy. How much energy does that represent in kilocalories?

ΔE values obtained by bomb calorimetry can be converted to give accurate ΔH values.

40.0 g of ice cubes at 0.0°C are combined with 150 g of liquid water at 20.0°C in a coffee cup calorimeter. Calculate the final temperature reached, assuming no heat loss or gain from the surroundings. (Data: specific heat capacity of H₂O(l), c = 4.18 J/g·°C; H₂O(s) → H₂O(l) ΔH = 6.02 kJ/mol)

In a reaction with high energy reactants and low energy products, q is negative.

Calculate the enthalpy change for the reaction NO(g) + O(g) → NO₂(g) From the following data: NO(g) + O₃(g) → NO₂(g) + O₂(g) ΔH = −198.9 kJ O₃(g) → 1.5O₂(g) ΔH = −142.3 kJ O₂(g) → 2O(g) ΔH = 495.0 kJ

An ideal gas (the system) is contained in a flexible balloon at a pressure of 1 atm and is initially at a temperature of 20°C. The surrounding air is at the same pressure, but its temperature is 25°C. When the system has equilibrated with its surroundings, both systems and surroundings are at 25°C and 1 atm. In changing from the initial to the final state, which one of the following relationships regarding the system is correct?

The enthalpy (H) of liquid water is greater than that of the same quantity of ice at the same temperature.

The specific heat capacity c of a metal is approximately related to its molar massℳ as follows: c ×ℳ = 3R, where R is the universal gas constant, 8.314 J/mol·K. Use this relationship to identify the metal which has a specific heat capacity of 0.900 J/g·K.

A system that undergoes an adiabatic change and has work done on it by the surroundings has

A 275-g sample of nickel at 100.0°C is placed in 100.0 mL of water at 22.0°C. What is the final temperature of the water? Assume that no heat is lost to or gained from the surroundings. Specific heat capacity of nickel = 0.444 J/(g·K)

Which one of the following relationships is always correct?

A common laboratory reaction is the neutralization of an acid with a base. When 50.0 mL of 0.500 M HCl at 25.0°C is added to 50.0 mL of 0.500 M NaOH at 25.0°C in a coffee cup calorimeter, the temperature of the mixture rises to 28.2°C. What is the heat of reaction per mole of acid? Assume the mixture has a specific heat capacity of 4.18 J/(g·K) and that the densities of the reactant solutions are both 1.00 g/mL.