1. When 1 mole of H 2 (g) reacts with Cl 2 (g) to form HCl(g) according to the f
ID: 901046 • Letter: 1
Question
1. When 1 mole of H2(g) reacts with Cl2(g) to form HCl(g) according to the following equation, 185 kJ of energy are evolved.
Is this reaction endothermic or exothermic? _________
What is the value of q? _______ kJ
2. When 1 mole of CO(g) reacts with H2(g) to form CH4(g) and H2O(g) according to the following equation, 206 kJ of energy are evolved.
Is this reaction endothermic or exothermic? _________
What is the value of q? _______ kJ
3.
When HCl(g) reacts with O2(g) according to the following reaction, 28.6 kJ of energy are evolved for each mole of HCl(g) that reacts. Complete the following thermochemical equation.
4. When Fe(s) reacts with Cl2(g) according to the following reaction, 400 kJ of energy are evolved for each mole of Fe(s) that reacts. Complete the following thermochemical equation.
Explanation / Answer
1. When 1 mole of H2 reacts with 1 mole of Cl2 to form 2 moles of HCl some energy might be released or absorbed. If you look for the heat of formation of HCl you will find that is -92.3 KJ, the entalpies of Hydrogen and Cl2 are 0.
Also you can find that this reaction is an exothermic reaction.
When a reaction is exothermic it means that it releases energy and is expressed with a "minus" sign
This means that the heat of reaction for this particular case is
q= - 185 KJ
2. The same thing applies here, the statement says that energy is evolved so this means we have an exothermic reaction, let me show you using heat of formations.
Heat of formation of products:
H2O = -241.81 KJ
CH4 = -74.87 KJ
Heat of formation of reactants
H2 = 0
CO = -110.53 KJ
Formula is
Heat of reaction = Heat of products - Heat of reactants
Heat of reaction = -74.87 + (-241.81) - ( -110.53) - 3 * 0 = -206 KJ
The negative sign means that the reaction is exothermic.
3. This reaction is exothermic hence the enthalpy is = -28.6 KJ.
This is for every mole of HCl, since we have 4 moles of HCl we only need to multiply 28.6 by 4 so we have:
-28.6 * 4 = -114.4 KJ
4. The statement says that energy is evolved so this means that we have an exothermic reaction -400 KJ for every mole of Fe, since we have 2 moles of Fe, entalphy is:
2 * - 400 KJ = -800 KJ
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