Homework Help: Chemistry

Posted by Steven on Tuesday, October 16, 2012 at 7:35pm.

In an exothermic reaction, is the heat of the reation less than, greater than, or equal to zero?

In an endothermic reaction, is the heat of reaction less than, greater than, or equal to zero?

Chemistry - genie_math, Tuesday, October 16, 2012 at 7:39pm
Exothermic reaction - Energy is released - so it is less than zero. [Negative value]

Endothermic reaction - Energy is absorbed - greater than zero [Positive value]

Examples -

Exothermic Reactions
C(s) + O2(g) → CO2(g); ΔH = –393.5 kJ
H2(g) + 1/2 O2(g) → H2O(l); ΔH = –285.8 kJ

Endothermic Reactions
N2(g) + O2(g) → 2NO(g); ΔH = +180.5 kJ > 0
C(s) + 2S(s) → CS2(l); ΔH = +92.0 kJ > 0

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