# How do I calculate ΔHrxfollowing reaction? CaO(s)+CO2(g)→CaCO3(s) Use the following reactions and given ΔH values: Ca(s)+CO2(g)+1/2O2(g)→CaCO3(s), ΔH= -812.8 kJ 2Ca(s)+O2(g)→2CaO(s), ΔH= -1269.8 kJ Express your answer using four significant figures.

Jan 31, 2017

Given
Ca(s)+CO_2(g)+1/2O_2(g)→CaCO_3(s), ΔH_1= -812.8 kJcolor(red)(... [1])
2Ca(s)+O_2(g)→2CaO(s), ΔH_2= -1269.8 kJcolor(red)(...[2])

We are to calculate the heat of following reaction.

$C a O + C {O}_{2} \to C a C {O}_{3} , \Delta {H}_{\text{rx}}$

Reversing the equation [2] and dividing both sides by $2$ we get
$C a O \to C a + \frac{1}{2} {O}_{2} , \Delta {H}_{3} = 634.9 k J \textcolor{red}{\ldots \left[3\right]}$

Now adding [1] and [3] we can get desired heat of raction

$\textcolor{b l u e}{C a O + C {O}_{2} \to C a C {O}_{3} , \Delta {H}_{\text{rx}} = \Delta {H}_{1} + \Delta {H}_{3}}$

$\implies \Delta {H}_{\text{rx}} = \left(- 812.8 + 634.9\right) k J$

$\implies \textcolor{red}{\Delta {H}_{\text{rx}} = - 177.9 k J}$