PAG 3 - Enthalpy Determination

Question 1

What is calorimetry?

Answer 1

Calorimetry is a process used to find the
amount of energy released or used in a
chemical reaction.

Question 2

What type of reaction releases energy to

the surroundings?

Answer 2

Exothermic

Question 3

What type of reaction takes in energy

from the surroundings?

Answer 3

Endothermic

Question 4

What is a neutralisation reaction?

Answer 4

A reaction between an acid and a base,

form a salt and water

Question 5

What is meant by the term standard

enthalpy change of neutralisation?

Answer 5

The enthalpy change that accompanies
the formation of 1 mole of water from a
neutralisation reaction under standard
conditions.

Question 6

Write the word and chemical equations
for the neutralisation reaction between
sodium hydroxide and hydrochloric acid

Answer 6

Hydrochloric acid + sodium hydroxide → sodium chloride + water
HCl + NaOH → NaCl + H2O

Question 7

The enthalpy change of a neutralisation
reaction is being investigated. Why might
this reaction carried out in a styrofoam
cup?

Answer 7

A styrofoam cup is a better thermal insulator
than a glass beaker so the less heat will be lost
to the surroundings meaning the calculated
temperature change is more accurate.

Question 8

What equation is used to calculate the

energy absorbed by the solution?

Answer 8

Q = mcΔT
m - mass of the solution (g)
c - specific heat capacity of the solution (the value for water is
used)
ΔT - temperature change (°C or K)
Q - heat energy (J)

Question 9

How is the enthalpy change of
neutralisation calculated from Q, the
energy absorbed by the solution?

Answer 9

Q ÷ mol
The number of moles can be calculated by using
mol = volume x concentration for the hydrochloric
acid used

Question 10

How can you find the maximum
temperature reached during a
neutralisation reaction?

Answer 10

Plot a graph of temperature (y axis)
against time (x axis) and extrapolating to
the time that the reactants were
combined

Question 11

Suggest 3 possible sources of error
when investigating the enthalpy change
of neutralisation. How could these errors
be reduced?

Answer 11

● Heat transfer to and from surroundings
● Incomplete combustion if using fuel
○ Bomb calorimeter could be used to combat these two
errors
● Inaccuracy in temperature measurement
○ Use an electronic thermometer

Question 12

Describe an experiment to investigate
the enthalpy change of neutralisation of
a reaction between hydrochloric acid and
sodium hydroxide

Answer 12

1. Add 25cm3 HCl(aq) to a polystyrene cup. Place the cup in a glass beaker. Measure 25cm3 NaOH(aq).
2. Start the timer. Record the initial temperature of the HCl at minute intervals for 3 minutes.
3. At the fourth minute, add the sodium hydroxide. Do not record the temperature.
4. Continue recording the temperature at minute intervals from 5 to 10 minutes. Stir the solution when measuring the temperature.