Enthalpy changes for reactions in solution

Question 1

Enthalpy changes for reactions in solution
The principle of these calorimetry experiments is to carry out the reaction with an

Answer 1

excess of one reagent and measure the temperature change over the course of a few minutes

The apparatus needed to carry out an enthalpy of reaction in solution calorimetry experiment is shown above

Question 2

Using a measuring cylinder place 25 cm3 of the 1.0 mol dm-3 …………… solution into the polystyrene cup

Answer 2

copper(II) sulphate

Question 3

step 2 Weigh about 6 g of zinc powder- as this is in excess //////////

Answer 3

as this is an excess there is no need to be very accurate

Question 4

step 3 Draw a table to record the initial

Answer 4

temperature and then the temperature and time every half minute up to 9.5 minutes

Question 5

step 4 Put a thermometer or temperature probe in the cup, stir, and record the temperature every ,,,,,,,,,, for 2½minutes

Answer 5

half minute

Question 6

At precisely 3 minutes, add the ………….. to the cup (DO NOT ……………..

Answer 6

zinc powder

RECORD THE TEMPERATURE AT 3MIN)

Question 7

step 6 stirring and record the temperature for an additional ………

Answer 7

6 mins

Question 8

For the purposes of the calculations, some assumptions are made about the experiment

Answer 8

That the specific heat capacity of the solution is the same as pure water, i.e. 4.18 J g-1 K-1

That the density of the solution is the same as pure water, i.e. 1 g cm-3

The specific heat capacity of the container is ignored

The reaction is complete

There are negligible heat losses

Question 9

Temperature correction graphs

REVISE THESEEEEEEEEEEEEEEEEE

Answer 9

For reactions which are not instantaneous there may be a delay before the maximum temperature is reached

During that delay the substances themselves may be losing heat to the surroundings, so that the true maximum temperature is never actually reached

To overcome this problem we can use graphical analysis to determine the maximum enthalpy change

Question 10

The steps to make a temperature correction graph are

Answer 10

Take a temperature reading before adding the reactants for a few minutes to get a steady value

Add the second reactant and continue recording the temperature and time

Plot the graph and extrapolate the cooling part of the graph until you intersect the time at which the second reactant was added