Question

given the reactions,
x(s) + \frac{1}{2}o_{2}(g) \to xo(s) \delta h = -804.7 kj
xco_{3}(s) \to xo(s) + co_{2}(g) \delta h = +367.5 kj
what is \delta h for this reaction?
x(s) + \frac{1}{2}o_{2}(g) + co_{2}(g) \to xco_{3}(s)
\delta h =

Explanation:

Step1: Reverse the second reaction

When we reverse the reaction \(XCO_3(s)\to XO(s)+CO_2(g)\) (\(\Delta H = + 367.5\space kJ\)), we get \(XO(s)+CO_2(g)\to XCO_3(s)\) and \(\Delta H=-367.5\space kJ\)

Step2: Add the two reactions

We have \(X(s)+\frac{1}{2}O_2(g)\to XO(s)\) (\(\Delta H=-804.7\space kJ\)) and \(XO(s)+CO_2(g)\to XCO_3(s)\) (\(\Delta H =- 367.5\space kJ\))
Adding them: \((X(s)+\frac{1}{2}O_2(g))+(XO(s)+CO_2(g))\to(XO(s)+XCO_3(s))\)
Cancel out \(XO(s)\) on both sides, we get \(X(s)+\frac{1}{2}O_2(g)+CO_2(g)\to XCO_3(s)\)
And \(\Delta H=(-804.7)+(-367.5)\)

Answer:

\(\Delta H=-1172.2\space kJ\)