Additional Practice Problems for Thermochemistry – Not required 1. Calculate the value of ∆H for the reaction: 2C (s) + H2 (g)  C2H2 (g) from the following thermochemical equations. C(s) + O2(g)  CO2 (g) H2(g) + ½ O2 (g)  H2O(l) 2C2H2 (g) + 5 O2(g)  4 CO2(g) + 2H2O(l)

∆H= - 393.5 kJ ∆H= -285.8 kJ ∆H= -2598.8 kJ

∆H = __________________________ 2. Hydrogen gas and fluorine gas react to produce hydrogen fluoride. Calculate the heat change (in kJ) for the conversion of 15.0 grams of hydrogen fluoride gas at constant pressure. H2(g) + F2(g)  2HF(g) ∆H = - 536 kJ

Heats of Physical Change Substance Formula Ammonia Ethanol Methane Water 3.

NH3 C2H5OH CH4 H2O

Heat of vaporization (kJ / mol) 23.4 43.5 35.3 40.7

Boiling point (K) 239.7 351.5 337.2 373.2

Heat of fusion (kJ / mol) 5.65 4.60 0.94 6.01

How much heat is required when 6.0 grams of water is vaporized at its boiling point?

Is this process endothermic or exothermic? ___________________________ 4.

How much heat is required to freeze 15.0 grams of water?

Is this process endothermic or exothermic? ____________________________

Freezing point (K) 195.3 158.7 90.7 273.2

Specific Heat Values: Substance Phase Copper solid Iron solid Lead solid Water liquid (25 °C) 5.

6.

Cp (J / goC) 0.385 0.450 0.127 4.1813

How much heat, in Joules, is required to raise the temperature of 500.0 g of iron from 25.0 C to 50.0 C?

During an experiment, 100.0 grams of water is placed in a calorimeter. The initial temperature of this water is 23.0oC. A sample of copper is heated and then placed in the water. The water heats up to a temperature of 58.0oC. What is the heat absorbed by the water in Joules?

Heat of Formation and Entropy Values:

Substance H2O (l) H2O (g) H2O2 (l) O2 (g) Al (s) Al2O3 (s)

∆H (kJ / mol) -286 -242 -187.8 0 0 -1670

∆S (J/mol) 70.0 189 110 205 28.3 51.0

7. Determine the ∆S for the reaction in which aluminum oxidizes to form aluminum oxide. 4Al (s) + 3 O2 (g) → 2 Al2O3 (s)

8.

Calculate the standard heat of formation (ΔH) for the decomposition of hydrogen peroxide. 2H2O2(l)  2H2O(l) + O2(g)