Some chemistry questions

1. If an energy term appears on the reactants side of a chemical equation the reaction must be
a. Exothermic
b. Endothermic


2. A combustion reaction usually involves
a. something being burned
b. the Synthesis of a hydrocarbon
c.the production of no new substances

3. Phosphoric acid decomposes to yield?

1. a) Endothermic.
Energy is required for the reaction to proceed forward.

2. a) something being burned.

3. PH3 + 2 O2