Bob adds heat to a substance. When enough heat is added, A. its particles move closer together and the substance becomes a gas.
B. its particles move farther apart and the substance becomes a solid.
C. its particles move farther apart and the substance becomes a gas.
D. its particles move closer together and the substance becomes a solid.

C. its particles move farther apart and the substance becomes a gas.

Explanation:

A. is wrong because moving closer together creates a solid, not a gas.

B. is wrong because moving father apart creates a gas, not solid.

C. is correct because moving farther apart creates a gas.

D. is wrong because when heat is added particles spread apart because they vibrate faster. Although, in a solid the particles are closer together.

- Just know the states of matter and how the particles move and that will help with this problem.

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.

i'm pretty sure its b i might be wrong though!