4co2(g) + 2h2o(g) 2c2h2(g) + 5o2(g) given: 118 kj 235 kj 470 kj 940 kj 1058 kj

You do these problems by finding the heat of formation of each compound, from a table.
Then the heat of reaction is the (sum of the heats of formation of the products) minus (sum of the heats of formation of the reactants).
In your case, the ∆Hrxn = 5∆Hf(O2(g)) + 2∆Hf(C2H2(g)) - 2∆Hf(H2O(g)) - 4∆Hf(CO2(g)).

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