Energy and Thermochemistry

Written Assignment 7: Energy and Thermochemistry
Answer all assigned questions and problems, and show all work.
1. Consider this reaction:
2CH3OH(l) + 3O2(g) → 4H2O(l) + 2CO2(g) ∆H = –1452.8 kJ/mol
a. Is this reaction endothermic or exothermic? (2 points)
b. What is the value of ∆H if the equation is multiplied throughout by 2? (2 points)
c. What is the value of ∆H if the direction of the reaction is reversed so that the products become the reactants and vice versa? (2 points)
d. What is the value of ∆H if water vapor instead of liquid water is formed as the product? (2 points)
(Reference: Chang 6.24)
2. The first step in the industrial recovery of zinc from the zinc sulfide ore is roasting,
that is, the conversion of ZnS to ZnO by heating:
2ZnS(s) + 3O2(g) → 3ZnO(s) + 2SO2(g)  ∆H = –879 kJ/mol
Calculate the heat evolved (in kJ) per gram of ZnS roasted. (5 points)
(Reference: Chang 6.25)
3. A 6.22 kg piece of copper metal is heated from 20.5 °C to 324.3 °C. Calculate the heat absorbed (in kilojoules) by the metal. Specific heat Cu = 0.385 J/g°C. (5 points)

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