Question

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Use the References to access important values if needed for this question. Given the standard enthalpy changes for the following two reactions: (1) 2Pb(s) + O2(g)—2PbO(s) AH° = -434.6 kJ (2) 2Zn(s) + O2(g)—>2ZnO(s) AH° = -696.6 kJ what is the standard enthalpy change for the reaction: (3) PbO(s) + Zn(s)—>Pb(s) + ZnO(s) AH° = ? kJ Submit Answer 1 question attempt remaining

Answer 1

Lets number the reaction as 1, 2, 3 from top to bottom
required reaction should be written in terms of other reaction
This is Hess Law
required reaction can be written as:
reaction 3 = -0.5 * (reaction 1) +0.5 * (reaction 2)

So, ΔHo rxn for required reaction will be:
ΔHo rxn = -0.5 * ΔHo rxn(reaction 1) +0.5 * ΔHo rxn(reaction 2)
= -0.5 * (-434.6) +0.5 * (-696.6)
= -131.0 KJ
Answer: -131.0 KJ