Question

Given these reactions, X ( s ) + 1 2 O 2 ( g ) ⟶ XO ( s ) Δ H = − 665.9 k J / m o l XCO 3 ( s ) ⟶ XO ( s ) + CO 2 ( g ) Δ H = + 190.1 k J / m o l what is Δ H for this reaction? X ( s ) + 1 2 O 2 ( g ) + CO 2 ( g ) ⟶ XCO 3 ( s )

Answer 1

ΔH of reaction is -856 kJ/mol

Step-by-step explanation:

The property ΔH is property which can be added to find the net change in enthalpy of reaction.

ΔH of first reaction is -665.9 kJ/mol

ΔH of second reaction is 190.1 kJ/mol

carefully looking at the third equation,

it is first reaction - second reaction.

thus, by Hess's law,

Hess's Law of Constant Heat Summation (or just Hess's Law) states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes.

ΔH of third reaction is =
`-665.9 - (190.1)`

ΔH = -856 kJ/mol