RQP 3: Investigation of how the rate of a reaction changes with temperature

Question 1

Describe the experiment which investigates how the rate of the reaction between sodium thiosulfate and hydrochloric acid changes with temperature

Answer 1

DISAPPEARING CROSS:
- measure 10cm^3 of 0.2 moldm^-3 hydrochloric acid and 10cm^3 of sodium thiosulfate in separate clean measuring cylinders and put the solutions in separate boiling tubes
- place the boiling tubes in a water bath at the first temperature
- place a conical flask over the centre of a large cross and add the sodium thiosulfate to the flask
- add the hydrcholirc aicd, swirl the solutions and start the stopwatch
- stop the clock when the cross disappears and note the time.
- repeat the experiment at different temperatures.

Question 2

What do we use as a measure of the rate of the reaction when doing a disappearing cross experiment

Answer 2

1/time (time taken for cross to disappear)

Question 3

What species causes the cross to disappear in the reaction between sodium thiosulfate and sulfuric acid

Answer 3

sulfur

Question 4

How do you analyse the results of the disppearing cross experiment to find its activation energy

Answer 4

• Using the Arrhenius equation
• lnk= -Ea/R(1/T) + lnA
• lnk is proportional to rate so can be replaced byb ln 1/t
• the gradient of the graph is equal to the -Ea/R