Exam 6: Thermochemistry Energy Flow and Chemical Change

Nitric acid, which is among the top 15 chemicals produced in the United States, was first prepared over 1200 years ago by heating naturally occurring sodium nitrate (called saltpeter) with sulfuric acid and collecting the vapors produced. Calculate ΔH°_rxn for this reaction. ΔH°_f [NaNO₃(s)] = -467.8 kJ/mol; ΔH°_f [NaHSO₄(s)] = -1125.5 kJ/mol; ΔH°_f [H₂SO₄(l) = -814.0 kJ/mol; ΔH°_f [HNO₃(g)] = -135.1 kJ/mol NaNO₃(s) + H₂SO₄(l) → NaHSO₄(s) + HNO₃(g)

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.

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

Which one of the following statements about standard states is incorrect?

The highly exothermic thermite reaction, in which aluminum reduces iron(III) oxide to elemental iron, has been used by railroad repair crews to weld rails together. 2Al(s) + Fe₂O₃(s) → 2Fe(s) + Al₂O₃(s) ΔH = -850 kJ What mass of iron is formed when 725 kJ of heat are released?

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?

The standard heat (enthalpy) of formation of graphite is zero.

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 equations represents the formation reaction of CH₃OH(l)?

Galena is the ore from which elemental lead is extracted. In the first step of the extraction process, galena is heated in air to form lead(II) oxide. 2PbS(s) + 3O₂(g) → 2PbO(s) + 2SO₂(g) ΔH = -827.4 kJ What mass of galena is converted to lead oxide if 975 kJ of heat are liberated?

Two solutions (the system), each of 25.0 mL volume and at 25.0°C, are mixed in a beaker. A reaction occurs between them, and the temperature rises to 35.0°C. After the products have equilibrated with the surroundings, the temperature is again 25.0°C and the total volume is 50.0 mL. No gases are involved in the reaction. Which one of the following relationships concerning the change from initial to final states (both at 25.0°C) is correct?

15.0 g of ice cubes at 0.0°C are combined with 150. g of liquid water at 70.0°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)

Use the following data to calculate the standard heat (enthalpy) of formation, ΔH_f°, of manganese(IV) oxide, MnO₂ (s). 2MnO₂(s) → 2MnO(s) + O₂(g) ΔH = 264 kJ MnO₂(s) + Mn(s) → 2MnO(s) ΔH = -240 kJ

Calculate the ΔH°_rxn for the following reaction. (ΔH°_f [SiO₂(s)] = -910.9 kJ/mol; ΔH°_f [SiCl₄(g)] = -657.0 kJ/mol; ΔH°_f [HCl(g)] = -92.3 kJ/mol; ΔH°_f [H₂O(g)] = -241.8 kJ/mol) SiO₂(s) + 4HCl(g) → SiCl₄(g) + 2H₂O(g)

The standard state of a substance in aqueous solution is a 1 M solution.

In which 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?

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

A system delivers 225 J of heat to the surroundings while delivering 645 J of work. Calculate the change in the internal energy, ΔE, of the system.

The combustion of glucose (C₆H₁₂O₆) with oxygen gas produces carbon dioxide and water. This process releases 2803 kJ per mole of glucose. When 3.00 mol of oxygen react in this way with glucose, what is the energy release in kcal? (Hint: Write a balanced equation for the combustion process.)