Question

4CO2(g) + 2H2O(g) 2C2H2(g) + 5O2(g) Given: 118 kJ 235 kJ 470 kJ 940 kJ 1058 kJ

Answer 1

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)).

Answer 2

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)).