Standard enthalpy change of neutralisation

Question 1

what is the standard enthalpy change of neutralisation?

Answer 1

the enthalpy change measured at 100kPa and a specific temperature, usually 298K, when one mole of water is produced by the neutralisation of an acid with an alkali.

Question 2

why is enthalpy change of neutralisation always negative?

Answer 2

because reactions between acids and alkalis are always exothermic, giving out heat.

Question 3

the equation for the standard enthalpy change of neutralisation of hydrochloric acid is

Answer 3

HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)

Question 4

the equation for the enthalpy change of neutralisation for sulfuric acid is

Answer 4

½ H2SO4 + NaOH(aq) → ½Na2SO4(aq) + H2O

Question 5

some acid-alkali combinations result in remarkably similar…….

Answer 5

enthalpy changes of neutralisation

Question 6

if we make the assumption that strong acids and alkalis are fully ionised in aqueous solution, then the reaction between them is simplified to:

Answer 6

H+(aq) + OH-(aq) → H2O(l)

Question 7

the five step method of finding the enthalpy change of neutralisation is;

Answer 7

1) using a pipette fitted with a safety filter, place 25.0cm3 of 1.00 mol dm-3 acid into an expanded polystyrene cup
2) measure the temperature of the acid
3) using a pipette, place 25.0cm3 of the alkali (usually a dilute solution of sodium hydroxide with a concentration of slightly greater than 1.00 mol dm-3) into a beaker
4) measure the temperature of the alkali
5) add the alkali to the acid, stir with the thermometer and measure the maximum temperature reached

Question 8

why is dilute sodium hydroxide of concentration slightly greater than 1.00 mol dm-3 used?

Answer 8

to ensure all of the acid is neutralised

Question 9

answers to enthalpy change of neutralisation calculations should be to

Answer 9

2 significant figures as ΔT is given to only two sig. figs.