Answer to Question #179316 in General Chemistry for mel

Question

Given Reactions:

X(s) + 1/2 O2 (g) -----> XO(s) ∆H = -815.9 kJ

XCO3 (s) -----> XO(s) + CO2 (g) ∆H = +357.1 kJ

what is ∆H for this reaction?

X(s) + 1/2 O2 (g) + CO2 (g) ----> XCO3 (s)

Answer 1

X(s)+1/2 O2(g)+CO2(g) --> XCO3(s)

this is the goal equation.

X(s) +1/2 O2(g) --> XO(s) ΔH=-815kJ

this equation is ok

XCO3(s) --> XO(s)+CO2(g)

this equation must be flipped and the H sign changed:

XO(s)+CO2(g) --> XCO3(s) ΔH=-357.1kJ

Sum equations to derive goal equation. Sum H's

= -815 + -357.1

= -1172.1kJ