3.1.4 Energetics

Question 1

Enthalpy change

Answer 1

Heat energy change under constant pressure

Question 2

Standard enthalpy change

Answer 2

Heat energy change under constant pressure of 100KPa and 298K

Question 3

What is an exothermic reaction

Answer 3

Heat energy is given out to the surroundings, products have less energy than the reactants and therefore have a negative change in heat energy (deltaH)
Bonds making

Question 4

What is an endothermic reaction

Answer 4

Heat energy is taken in from the surroundings, products have more energy than reactants and therefore have a positive change in heat energy (deltaH)
Bonds breaking

Question 5

Equation for change in heat energy

Answer 5

Sum of bond energies broken - sum of bond energies made

Question 6

Equation for energy change with symbols

Answer 6

Energy change = mass X heat capacity X temp change
Q = m X C X deltaT

Question 7

Why are values from an experiment of heat energy change different to the values in the data value book

Answer 7

Heat loss to the surroundings
Incomplete combustion

Question 8

What does hess’ law state

Answer 8

The total enthalpy change for a reaction is independent of the route taken

Question 9

Enthalpy change of formation

Answer 9

Enthalpy change when one mole of a compound is formed from its elements at standard states and standard conditions - 100 KPa and 298 K

Question 10

Equation of enthalpy change of formation

Answer 10

Enthalpy change = sum of products - sum of reactants

Question 11

Enthalpy change of combustion

Answer 11

Enthalpy change when one mole of a compound is burnt completely in oxygen under standard states and conditions -298K and 100KPa -

Question 12

Equation for enthalpy change of combustion

Answer 12

Enthalpy change = sum of reactants - sum of products