Chemical Energetics

Question 1

Hess’ Law

Answer 1

The enthalpy change accompanying a chemical reaction is the same REGARDLESS OF THE ROUTE by which the chemical change occurs, provided the INITIAL AND FINAL STATES ARE THE SAME.

Question 2

STANDARD enthalpy change of reaction

Answer 2

The energy change in a chemical reaction when MOLAR QUANTITIES OF REACTANTS specified in the chemical equation react to form products at STANDARD CONDITIONS

Question 3

Standard enthalpy change of formation of substance (this feels like the more general one to me because it could be any substance)

Answer 3

The energy change when ONE MOLE OF THE SUBSTANCE is formed from its CONSTITUENT ELEMENTS under standard conditions.

Question 4

Standard enthalpy change of combustion a substance

Answer 4

Is the energy evolved when one mole of a substance is COMPLETELY BURNT IN OXYGEN under standard conditions.

Question 5

Standard enthalpy change of neutralisation

Answer 5

Is the energy evolved when ONE MOLE OF WATER is formed from the neutralisation between an acid and a base under standard conditions. (omg neutralisation is exothermic)

Question 6

Standard enthalpy change of atomisation of an element

Answer 6

Is the energy ABSORBED when one mole of GASEOUS ATOMS is formed from the element under standard conditions.

Question 7

Bond energy

Answer 7

The AVERAGE energy that is absorbed to break one mole of covalent bonds in the GASEOUS STATE to form GASEOUS ATOMS under standard conditions.

Question 8

Bond dissociation energy

Answer 8

The energy required to break ONE MOLE OF A PARTICULAR COVALENT BOND in a SPECIFIC MOLECULE in the gaseous state to form gaseous atoms.

Question 9

Lattice energy of an ionic solid

Answer 9

Energy evolved when one mole of a SOLID IONIC COMPOUND is formed from its constituent GASEOUS IONS under standard conditions.

Question 10

First ionisation energy

Answer 10

The energy absorbed when one mole of GASEOUS atoms loses one mole of electrons to form one mole of singly charged GASEOUS cations.

Question 11

Second ionisation energy

Answer 11

The energy absorbed when one mole of singly charged gaseous cations loses one mole of electrons to form one mole of doubly charged gaseous cations.

Question 12

First electron affinity

Answer 12

The energy released when one mole of gaseous atoms acquires one mole of electrons to form one mole of singly charged gaseous anions.

Question 13

Second electron affinity

Answer 13

The energy absorbed when one mole of singly charged gaseous anions acquires one mole of electrons to form one mole of doubly charged gaseous anions.

Question 14

Standard enthalpy change of hydration of an ion

Answer 14

Energy EVOLVED when one mole of gaseous ions is HYDRATED under standard conditions.

Question 15

Standard enthalpy change of solution of a substance

Answer 15

Energy change when one mole of a substance is completely dissolved in a solvent to form an INFINITELY DILUTE SOLUTION under standard conditions.

Question 16

Define entropy

Answer 16

Measures the DEGREE OF DISORDER or randomness in a system. It is reflected in the number of ways the energy in a system can be distributed through the motion of the particles.

Question 17

When does entropy change?

Answer 17

• When there is a change in phase*
• When there is a change in temperature
• When there is a change in the number of particles*
• When a gaseous system faces an expansion of volume
• When particles are mixed
  Depends on the number of ways to distribute the particles and energy