Heat — Quiz

Question 3 • Physical Science

Which reaction is exothermic?

Answer

cap n sub 2 plus cap o sub 2 plus 181 kJ rightarrow 2 NO

CH sub 4 plus 2 cap o sub 2 rightarrow CO sub 2 plus 2 cap h sub 2 cap o plus 891 kJ

2 cap h sub 2 cap o plus 286 kJ rightarrow 2 cap h sub 2 plus cap o sub 2

cap n sub 4 NO sub 3 plus cap h sub 2 cap o plus 25 kJ rightarrow NH sub 4 raised to the plus aq power plus NO sub 3 raised to the negative aq power

Explanation

An exothermic reaction releases heat, so the energy appears on the products side of the equation. In choice D, 891 kJ is produced along with carbon dioxide and water, so the reaction is exothermic. In choices A, B, and C, heat is on the reactants side, meaning those reactions absorb energy.

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