enthalpy change

Question 1

define enthalpy

Answer 1

change in heat energy at a constant pressure

Question 2

what are the standard conditions for enthalpy change?

Answer 2

100kPa
298 K

Question 3

what does it mean if enthalpy change is positive?

Answer 3

endothermic
energy has been taken in from the surroundings

Question 4

what does it mean if enthalpy change is negative?

Answer 4

exothermic
energy is released into surroundings

Question 5

what is activation energy?

Answer 5

minimum energy required for a reaction to take place between 2 colliding reactant particles

Question 6

define ‘standard enthalpy change of reaction’

Answer 6

the enthalpy change associated with a stated reaction
quantities of substances in standard states react completely under standard conditions

Question 7

define ‘enthalpy change of formation’

Answer 7

the enthalpy change when one mole of a substance is produced from its elements in their standard states under standard conditions

Question 8

define ‘enthalpy change of combustion’

Answer 8

the enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions

Question 9

define ‘enthalpy change of neutralisation’

Answer 9

the enthalpy change when solutions of acid and alkali recat together under standard conditions to produce one mole of water

Question 10

describe an exothermic reaction profile diagram

Answer 10

• reactants higher than products
• arrow from reactants to products going downwards

Question 11

decribe an endothermic reaction profile diagram

Answer 11

• products higher than reactants
• arrow from reactants to products going upwards