Heat of combustion of CH 4 , C 2 H 6 , C 2 H 4 and C 2 H 2 are − 212.8 , − 373.0 , − 337.0 and − 310.5 kcal mol − 1 respectively at the same temperature. The best fuel among these gases

Question

Heat of combustion of CH 4 ​ , C 2 ​ H 6 ​ , C 2 ​ H 4 ​ and C 2 ​ H 2 ​ are − 212.8 , − 373.0 , − 337.0 and − 310.5 kcal mol − 1 respectively at the same temperature. The best fuel among these gases is (Atomic masses: H = 1 , C = 12 )

TestHub · Accepted Answer

To determine the best fuel, calculate the fuel value (heat of combustion per gram) for each gas.

1. Calculate molar masses:

CH₄: $12 + 4 (1) = 16 g / m o l$

C₂H₆: $2 (12) + 6 (1) = 30 g / m o l$

C₂H₄: $2 (12) + 4 (1) = 28 g / m o l$

C₂H₂: $2 (12) + 2 (1) = 26 g / m o l$

2. Calculate fuel values:

CH₄: $\frac{- 212.8 k c a l / m o l}{16 g / m o l} = - 13.3 k c a l / g$

C₂H₆: $\frac{- 373.0 k c a l / m o l}{30 g / m o l} = - 12.43 k c a l / g$

C₂H₄: $\frac{- 337.0 k c a l / m o l}{28 g / m o l} = - 12.04 k c a l / g$

C₂H₂: $\frac{- 310.5 k c a l / m o l}{26 g / m o l} = - 11.94 k c a l / g$

The best fuel has the highest heat of combustion per gram (most negative value). CH₄ has the highest fuel value.

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