2.4 Chemical reactions and energy

Question 1

What is an exothermic reaction?

Answer 1

A reaction that transfers energy to the surroundings.

and where the products have a greater bond energy than the reactants

Question 2

What is an endothermic reaction?

Answer 2

• A reaction that absorbs energy from the surroundings.

- (and where the reactants have a greater bond energy than the products)

Question 3

What is the units for bond energy?

Answer 3

KJ/mol

Question 4

What happens in a chemical reaction in terms of energy?

Answer 4

1) When bonds break, they absorb energy equivalent to their bond energy (bond energy of reactants= energy in) (Endothermic)
2) When new bonds form, energy is released equivalent to the total bond energy (bond energy of products= energy out) (Exothermic).

Question 5

What is the equation for the change in energy for a chemical reaction? What is it’s meaning?

Answer 5

Bond energy reactants (In) - Bond energy of products (Out) = Energy change (for the molecule)

A negative change means released energy so exothermic
A positive change means absorbed energy so endothermic

Question 6

What is the name given to the difference in energy between products and reactants?

Answer 6

Enthalpy Change

Question 7

What is the bond energy?

Answer 7

The amount of energy it takes to break one mole of bonds.