Enthalpy change in reaction

Chemistry Level 2

If 23 grams of ethanol, C X 2 H X 5 O H ( l ) \ce{C2 H5OH}(l) is fully combusted, 683.4 kJ 683.4\text{ kJ} of heat is generated. The thermochemical equation for this reaction is as follows:

C X 2 H X 5 O H ( l ) + 3 O X 2 ( g ) → 2 C O X 2 ( g ) + 3 H X 2 O ( l ) \ce{C2H5OH}(l) + 3\ce{O2}(g) \ce{->} 2\ce{CO2}(g) + 3\ce{H2O}(l)

Find the value of Δ H \Delta H in terms of kJ/mol \text{kJ/mol} .

You are given that the molecular weight of C X 2 H X 5 O H ( l ) \ce{C2 H5OH}(l) is 46.

683.4 1366.8 -1366.8 -683.4

Lakshan Dumpa by Lakshan Dumpa , 24, India

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2 solutions

Bernardo Sulzbach
Jun 19, 2014

We know that 683.4 kJ is the heat liberated from the complete combustion of 0.5 mol of ethanol. So 1.0 mol of ethanol generates 1366.8 kJ when burned. It is exothermic, so Δ H \Delta{}H is negative.

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23 g -------- 683,4 KJ

46 g -------- X

X = (46 g × 683,4 KJ)/ 23g = 1366,8 KJ

If is a exotermic reaction, ∆H <0, and 46 g/mol is the MM of ethanol, the ∆H = (-)1366,8 KJ/1 mol = -1366,8 KJ/mol.

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