Enthalpy

Question 1

Define enthalpy

Answer 1

It is a measure of the heat energy in a chemical system. It can be thought of as the energy stored within bonds. It cannot be measured but enthalpy changes can.

Question 2

What happens in a endothermic enthalpy profile?

Answer 2

The products have a higher enthalpy than the reactants.
Triangle H+

Question 3

What happens in a exothermic enthalpy profile?

Answer 3

The reactants have a higher enthalpy than the products.
Triangle H-

Question 4

Define the enthalpy change of formation. (Triangle F H circle with line through it.)

Answer 4

Enthalpy change when 1 mole of a substance is formed from its elements under standard conditions with all reactants and products in their standard states.

Question 5

Define the enthalpy change of combustion. (Triangle C H circle with line through it.)

Answer 5

Enthalpy change when 1 mole of a substance is completely burned in oxygen, under standard conditions, with all reactants and products in their standard states.

Question 6

Define the enthalpy change of neutralisation. (Triangle neut H circle with line through it.)

Answer 6

Enthalpy change when 1 mole of water is formed from reaction between an acid and an alkali, under standard conditions, with all reactants and products in their standard states.

Question 7

Define the standard enthalpy of reaction (Triangle r H circle wit line through it)

Answer 7

Enthalpy change when molar quantities of reactants as stated in the equation, react together under standard conditions, with all reactants and products in their standard states.