The enthalpy change for the reaction between tungsten (W) and graphite is diffic

Question

The enthalpy change for the reaction between tungsten (W) and graphite is difficult to measure directly because the reaction occurs at 1400 degree C: W (s) + C (s, graphite) rightarrow WC (s) However, the heats of reactions of the elements and of tungsten carbide with oxygen can be measured and are given below: 2 W (s) + 3 O_2 (g) rightarrow 2 WO_3 (s) delta H = -1680.6 kJ C (s, graphite) + O_2 (g) rightarrow CO_2 (g) delta H = -393.5 kJ 2 WC (s) + 5 O_2 (g) rightarrow 2 WO_3 (s) + 2 CO_2 (g) delta H = -2391.6 kJ The enthalpy of reaction, delta H, for the formation of tungsten carbide, WC (s), from its elements is: -3.8 kJ -38.0 kJ -380.0 kJ +380.0 kJ none of these

Explanation / Answer

del H = eqn 1 +2* eq 2- eq 3

2 (W+ S--->WC)

del H = -1680.6-2*393.5 -(-2391.6) = 76 KJ

2 (W+ S--->WC) =  -76 KJ

(W+ S--->WC) = - 76/2 = -38 KJ

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