Enthalpy Changes

Question 0

What is an exothermic reaction?

Answer 0

One where the products have less enthalpy than the reactants, so excess energy is released as heat
Eg oxidation of fuels by combustion

Question 1

Endothermic processes require…
Why do they require this?
Give one example of an endothermic reaction

Answer 1

An input of energy
The products have more energy than the reactants, so energy must be absorbed from the surroundings
Eg the thermal decomposition of calcium carbonate

Question 2

Give one natural process that is exothermic

Answer 2

Respiration

Question 3

Give one natural process that is endothermic

Answer 3

Photosynthesis

Question 4

Standard conditions definition

Answer 4

1atm, 25*C, 1.0 moldm^-3

Question 5

Enthalpy change of reaction definition

Answer 5

The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states

Question 6

Standard enthalpy change of combustion definition

Answer 6

The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states

Question 7

Standard enthalpy change of formation definition

Answer 7

The enthalpy change that takes place when one mole of a compound is formed from it’s constituent elements in their standard states under standard conditions

Question 8

Bond breaking is…

Answer 8

Endothermic

Question 9

Bond making is…

Answer 9

Exothermic

Question 10

Average bond enthalpy definition

Answer 10

The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species