Video Transcript
Which of the following is the best
definition of an endothermic reaction? (A) Heat is absorbed from the
surroundings and there is a decrease in the total bond energy. (B) Heat is released to the
surroundings and there is a decrease in the total bond energy. (C) Heat is absorbed from the
surroundings and there is an increase in the total bond energy. (D) Heat is released to the
surroundings and there is an increase in the total bond energy. (E) Heat is absorbed from the
surroundings and there is no change in the total bond energy.
To help us answer this question,
let’s break down the word “endothermic.” “Thermic” comes from the Greek
meaning heat. Endo- also comes from Greek and
means “in.” So, we could say that an
endothermic reaction is a reaction that takes in heat, or in other words a reaction
that absorbs heat from the surroundings, although technically an endothermic
reaction is a reaction that absorbs energy from the surroundings in any form,
including heat, light, and sound. From this information, we can
eliminate answer choices (B) and (D), as we know that endothermic reactions absorb
energy from the surroundings.
Now we need to consider what
happens to the total bond energy during an endothermic reaction. Typically in chemical reactions,
energy needs to be absorbed in order for bonds to break, and energy is released when
bonds form. We know that in an endothermic
reaction, energy is absorbed from its surroundings. As bond breaking and bond forming
both occur during a chemical reaction, in order for the reaction to be endothermic,
more energy must be absorbed than is released during the reaction.
Let’s see how this relates to the
bond energy of the reactants and products in a chemical reaction. At the start of the reaction, the
reactants have a certain amount of energy. In an endothermic reaction, more
energy will be absorbed than is released during the reaction. This means that the products will
have a higher total bond energy than the reactants. So, during an endothermic reaction,
there is an increase in the total bond energy.
Therefore, the best definition of
an endothermic reaction is answer choice (C). Heat is absorbed from the
surroundings and there is an increase in the total bond energy.
