The data below refers to gas phase reaction at constant pressure at 25°C. CH3-CH3 - CH3-CH2 + H; δ H_1 = +420 kJ mol^-1 and CH3-CH2 - CH2=CH2 + H; δ H_2 = +168 kJ mol^-1. From these data, the enthal

Question

The data below refers to gas phase reaction at constant pressure at 25°C. CH3-CH3 -> CH3-CH2 + H; δ H_1 = +420 kJ mol^-1 and CH3-CH2 -> CH2=CH2 + H; δ H_2 = +168 kJ mol^-1. From these data, the enthalpy change δ H for the reaction: 2CH3-CH2 -> CH3-CH3 + CH2=CH2 is

Prashant Kotian · Accepted Answer

Correct answer: C. We want: 2CH3-CH2 -> CH3-CH3 + CH2=CH2. Let's use the given reactions: (1) CH3-CH2 + H -> CH3-CH3; δ H = -420 kJ (reverse of 1st). (2) CH3-CH2 -> CH2=CH2 + H; δ H = +168 kJ. Adding (1) and (2): 2CH3-CH2 -> CH3-CH3 + CH2=CH2; δ H = -420 + 168 = -252 kJ.

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