Given the following data:

Question

Given the following data:
MnO(s) + H2(g) Mn(s) + H2O(l), H = 100 kJ
MnO2(s) + 2 H2(g) Mn(s) + 2 H2O(l), H = -52 kJ
use Hess's law to calculate the heat of the reaction
MnO2(s) + H2(g) MnO(s) + H2O(l)

Answer 1

Target equation: MnO2(s) + H2(g) --> MnO(s) + H2O(l)

Given:

(1). MnO(s) + H2(g) --> Mn(s) + H2O(l), H = 100 kJ

(2). MnO2(s) + 2 H2(g) --> Mn(s) + 2 H2O(l), H = -52 kJ

Procedure:

reverse eq (1): Mn(s) + H2O(l) --> MnO(s) + H2(g) ... ∆H = -100 kJ

copy eq (2): MnO2(s) + 2 H2(g) --> Mn(s) + 2 H2O(l) ... ∆H = -52 kJ

Add together to get...

Mn(s) + H2O(l) + MnO2(s) + 2 H2(g) --> MnO(s) + H2(g) + Mn(s) + 2 H2O(l)

Combine and/or cancel like terms to get...

MnO2(s) + H2(g) --> MnO(s) + H2O(l) .. Target equation

∆H = -100 kJ + - 52 kJ

∆H = -152 kJ