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Ch.5 - Thermochemistry

Chapter 5, Problem 68

Dimethyl ether, CH3OCH3(𝑔), is an industrially useful organic compound that is a gas at room temperature. Consider the following balanced thermochemical equations:

CH3OCH3(g) + 3 O2(g) β†’ 2 CO2(g) + 3 H2O(g) Ξ”HΒ° = βˆ’1328 kJ          

CH4(g) + 2 O2(g) β†’ CO2(g) + 2 H2O(g) Ξ”HΒ° = βˆ’802 kJ      

2 C2H6(g) + 7 O2(g) β†’ 4 CO2(g) + 6 H2O(g) Ξ”HΒ° = βˆ’2855 kJ

a. All three of the above reactions produce H2O(𝑔). If they were written to produce H2O(𝑙) instead, would the values of Δ𝐻° become more negative, become less negative, or stay the same?

b. By using Hess’s law and the reactions provided, calculate Δ𝐻° for the following balanced reaction between dimethyl ether and methane to produce ethane and water:

CH3OCH3(g) + 2 CH4(g) β†’ 2 C2H6(g) + H2O(g)