Enthalpy Changes

Question 1

What does the First Law of Thermodynamics state?

Answer 1

Energy can neither be destroyed nor created but it can be converted from one form to another

Question 2

Examples of exothermic reactions?

Answer 2

Combustion
Respiration

Question 3

Examples of endothermic reactions?

Answer 3

Photosynthesis
Thermal decomposition

Question 4

Define enthalpy

Answer 4

Measure of the heat content of a substance at constant pressure

Question 5

How do you calculate enthalpy change?

Answer 5

Enthalpy of products - Enthalpy of reactants

Question 6

Exothermic is what type of enthalpy?

Answer 6

Negative

Question 7

Endothermic is what type of enthalpy?

Answer 7

Positive

Question 8

A substance under the conditions of 100kPa and 298K is said to be in what state?

Answer 8

Its standard state

Question 9

Define Standard Enthalpy of formation

Answer 9

The enthalpy change when one mole of a compound is formed in its standard state from its elements in their standard states

Question 10

Standard enthalpy of formation is usually endothermic or exothermic?

Answer 10

Exothermic

Question 11

Define Standard enthalpy of combustion

Answer 11

The enthalpy change when one mole of a substance undergoes complete combustion under standard conditions

Question 12

Is standard enthalpy of combustion endorhermic or exothermic?

Answer 12

Exothermic

Question 13

Define enthalpy of neutralization

Answer 13

The enthalpy change when one mole of water is formed from its ions in dilute solution

Question 14

Is enthalpy of neutralisation endothermic or exothermic?

Answer 14

Exothermic

Question 15

Define enthalpy of atomisation

Answer 15

The enthalpy change when a substance in its standard state is totally separated into one mole of gaseous atoms

Question 16

Is enthalpy of atomisation endothermic or exothermic?

Answer 16

Endothermic

Question 17

What is bond dissociation enthalpy?

Answer 17

The energy required to break one mole of covalent bonds to form gaseous atoms

Question 18

Define lattice formation enthalpy

Answer 18

The enthalpy change when one mole of a substance in a lattice is formed in its gaseous ions

Question 19

Define enthalpy of solution

Answer 19

The enthalpy change when one mole of an ionic substance dissolves completely in water to give a solution of infinite dilution

Question 20

Define enthalpy of hydration

Answer 20

The enthalpy change when one mole of gaseous ions dissolves in water to give a solution of infinite dilution