Calculate the Enthalpy of reaction, Hrxn , for the following reaction. 2 C2H6 (g

Question

Calculate the Enthalpy of reaction, Hrxn , for the following reaction.

2 C2H6 (g) + 7 O2 (g) 4CO2 (g) + 6 H2O (l)

a. Using Hess’s Law, the following reactions can be used to determine the enthalpy of reaction. Determine if the reactions must be reversed or multiplied by a factor before combining the reactions.

2CH4(g) C2H4(g)+2H2(g)  Ho =201.9kJ

CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O(l) Ho= -890.3 kj

C2H4(g)+H2(g) =C2H6(g) Ho=-137.0kJ

H2 (g) + 12 O2 (g) = H2O(l) Ho=-285.8 kJ

Rewrite each reaction below before combining the four reactions.

What is the Hrxn for the combustion of ethane gas?

Is the reaction exothermic or endothermic?

Explanation / Answer

2 C2H6 (g) + 7 O2 (g) =====> 4CO2 (g) + 6 H2O (l)

----------------------------------------------------------------------------------------

2C2H6(g) ========> 2C2H4(g)+2H2(g)   Ho= 274.0kJ

4CH4 (g) + 8 O2 (g) ==========>4 CO2 (g) + 8H2O(l) Ho= -3561.2 kj

2H2O(l)   ======> 2H2 (g) + O2 (g) Ho=285.8 kJ

2C2H4(g)+4H2(g) ========> 4CH4(g)   Ho =201.9kJ

Hence sum up all Ho values

It will give -2799.5 KJ

Hrxn for the combustion of ethane gas is -2799.5 KJ

Since it is with negative sign it is a exothermic reaction

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