Determining enthalpy change of reaction

Question 1

What is enthalpy change of reaction?

Answer 1

The enthalpy change when a reaction takes place in the molar quantities shown by the balanced equation under standard conditions with all chemicals in standard states

Question 2

What type of reaction are we doing?

Answer 2

One that isn’t neutralisation, formation or combustion
Eg reacting magnesium with copper sulfate

Question 3

Step 1

Answer 3

With a polystyrene cup in a beaker, pour 100cm3 of 1moldm-3 copper sulfate solution

Question 4

Step 2

Answer 4

Take readings every 30s

Question 5

Step 3

Answer 5

At 1 min 30s, add Mg powder and stir with thermometer

Question 6

Step 4

Answer 6

Continue to take temp readings every 30s until 5 mins

Question 7

Step 5

Answer 7

Plot the temp change on a graph, with time on x axis and temperature on y axis

Question 8

How can we find an accurate temp change using this graph?

Answer 8

Extrapolate from the start of the reaction (when the mg was added at 1min 30s) upwards
Then extrapolate the point where temp begins to decrease
Point these lines meet = the maximum temp reached

Question 9

Why do we use a graph to find the maximum temperature reached?

Answer 9

To account for the heat loss at all points of the reaction
To find the maximum temperature reached had no cooling occurred.

Question 10

How to find enthalpy change of formation of this reaction?

Answer 10

Q = mc△T
Mass of copper sulfate solution x specific heat capacity x temperature change

Question 11

What values have we found in this experiment to find enthalpy change?

Answer 11

Mass of copper sulfate solution = 100
Shc = 4.18
Temp change = found from graph

Question 12

How to find the enthalpy change PER MOL?

Answer 12

Divide the enthalpy change by the mol of magnesium that reacted