3.3 chemical energy

Question 1

What is enthalpy

Answer 1

a measure of the chemical energy in a substance

Question 2

What is an exothermic reaction?

Answer 2

a reaction that releases heat energy

Question 3

What may happen with exothermic reactions in industry?

Answer 3

may require heat to be removed to prevent the temperature rising.

Question 4

What is an endothermic reaction?

Answer 4

a reaction that takes in heat energy.

Question 5

What may happen with endothermic reactions in industry?

Answer 5

may incur costs in supplying heat energy in order to maintain the reaction rate.

Question 6

How can the enthalpy change of a reaction be calculated?

Answer 6

the quantity of heat energy released

Question 7

How can the quantity of heat energy released be determined

Answer 7

Eh=cmΔT

Question 8

What is the enthalpy of combustion of a substance?

Answer 8

the enthalpy change when one mole of the substance burns completely in oxygen.

Question 9

What does Hess’s law state?

Answer 9

the enthalpy change for a chemical reaction is independent of the route taken.

Question 10

What is the molar bond enthalpy?

Answer 10

the energy required to break one mole of bonds in a diatomic molecule.

Question 11

What is a mean molar bond enthalpy?

Answer 11

the average energy required to break one mole of bonds, for a bond that occurs in a number of compounds.

Question 12

What can bond enthalpies be used for?

Answer 12

-to estimate the enthalpy change occurring for a gas phase reaction

Question 13

How do you calculate the enthalpy change for a gas phase reaction?

Answer 13

• calculate the energy required to break bonds in the reactants
• calculate the energy released when new bonds are formed in the products
• find the difference from the reactants to the products