Thermochemical Equations Practice Problems

Acetylene (C₂H₂) is a gas used for welding. Combustion of acetylene releases 1301.1 kJ/mol. Calculate the energy (in kilojoules) released in burning 65.0 g acetylene.

For the sublimation of dry ice, CO₂(s) → CO₂(g), ΔH = +25.0 kJ/mol. Calculate the energy (in kilojoules) required for the sublimation of 8.5 g of dry ice.

Sucrose (C₁₂H₂₂O₁₁) is the end product of photosynthesis and is found in a lot of food plants. The complete combustion of sucrose releases 5155.7 kJ/mol of energy. Calculate the amount of energy required to produce 18.0 g of sucrose.

Condensing ethanol vapor to liquid releases 38.56 kJ/mol of heat. Calculate the energy released when 56 mL of ethanol is condensed.

The melting of potassium requires 2.33 kJ/mol. Calculate the amount of energy required to melt 26.3 g of potassium.

Lithium oxide can be obtained by the decomposition of lithium peroxide: 2 Li₂O₂(s) → 2 Li₂O(s) + O₂(g); ΔH°rxn = –561.5 kJ/mol

Calculate the energy (in kilocalories) released when 25.0 g lithium oxide is produced.

The ΔH for the formation of hydrogen peroxide from its elements is —32.58 kcal/mol ( —136.3 kJ/mol). In the formation of 0.850 mol of hydrogen peroxide, how much energy in kcal and kJ is released?

For the neutralization of NaOH and HCl: NaOH(aq) + HCl(aq) → H₂O(l) + NaCl(aq)     ΔH = –57.9 kJ/mol

In a coffee cup calorimeter, 100 mL of 0.100 M NaOH was neutralized with 100 mL of 0.100 M HCl. If both solutions were initially at 25 °C, determine the final temperature of the solution. Assume that the density and heat capacity of the solution is the same as that of water.

Lead ions can be precipitated using a solution of bromide ions: Pb²⁺(aq) + 2 Cl^–(aq) → PbCl₂(s)     ΔH°_f = –336.0 kJ/mol

Calculate ΔH for the formation of 5.15 g PbCl₂.

Calculate the mass of water required to evaporate from your skin to exhaust 2.15×10⁵ J of heat from your body.

H₂O(l) → H₂O(g)            ΔH_vap = 40.7 kJ/mol