Which statement about exothermic reactions is accurate?

as reactants form products, the potential energy decreases.

as reactants form products, the potential energy increases.

thermal energy is transferred from the product to the reacting substances.

thermal energy is transferred from the surroundings to the reacting substances.

Answer is: As reactants form products, the potential energy decreases.

There are two types of reaction:

1) Endothermic reaction (chemical reaction that absorbs more energy than it releases).

2) Exothermic reaction (chemical reaction that releases more energy than it absorbs).

For example, balanced chemical reaction:  

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O  ΔrH= -1370 kJ/mol.

This reaction is exothermic reaction (heat is released), so products have less potential energy and energy is transerred to surroundings.

answer: - 3.) the oxidation state of nitrogen in no changes from +2 to 0, and the oxidation state of carbon in co changes from +2 to +4 as the reaction proceeds.

solution: - as per the rules, oxidation number of oxygen in its compounds is -2. the sum of oxidation numbers of all the elements of a molecule or compound is zero.

also, the oxidation number in elemental form is zero.

in no, the oxidation number of o is -2 so the oxidation number of n is +2 so that the sum is zero.

similarly, the oxidation number of c in co is +2 and o is -2.

on product side the oxidation number of n is 0 as it is in the elemental form() .

oxidation number of c in carbon dioxide is +4 as there are two oxygen in it and we know that each oxygen is -2.

so, oxidation number of n is changing from +2 to 0 and the oxidation number of c is changing from +2 to +4.

since nitrogen is reduced and hence no is acting as an oxidizing agent. carbon is oxidized and so co is acting as a reducing agent.

so, the right choice is number 3.)the oxidation state of nitrogen in no changes from +2 to 0, and the oxidation state of carbon in co changes from +2 to +4 as the reaction proceeds.