Effect of temperature on reaction rate

Question 1

Identify the insoluble solid and colourless gas present in the reaction between sodium thiosulfate and dilute hcl

Answer 1

Insoluble solid : sulfur

Colourless gas : sulphur dioxide

Question 2

Outline the experimental procedures you would follow in order to show the effect of temperature on reaction rate

Answer 2

Place a conical flask on a piece of paper marked with an X
Place fixed volume of a given concentration of thiosulfate in the flask
Place in a water bath to keep temperature constant
Add fixed volume of HCL to the flask and note the time taken for sulfur to obscure x, swirl conical flask, reaction is finished
Rate of reaction for concentration is inversely promotional to the time taken
Repeat the experiment with different temperatures [water bath]

Question 3

Give two reasons why the rate of reaction between sodium thiosulphate solution and dilute hydrochloric acid increases with temperature

Answer 3

Increased temperature

• inc kinetic energy of particles which results in a greater number of collisions and increase in number of successful collisions and therefore an increased rate of reaction
• inc average kinetic energy of molecules which results in more molecules reaching required activation energy for the reaction which results in increase rate of reaction

Question 4

Describe and explain the change observed in the conical flask during the reaction

Answer 4

Sulfur precipitates to yellow smokey appearance

Question 5

Explain how the change in the flask was used to obtain the reaction times

Answer 5

X under conical flask obscured - reaction finished

Question 6

Describe the relationship of temperature vs 1/t

Answer 6

as temp increases, the number of colliding particles. At a point, it will reach threshold level of activation energy and therefore resulting in more effective collisions and explains the steepness

Question 7

What would the effect on reaction times if the experiment were repeated using 0.025M of sodium thiosulfate rather than 0.05M

Answer 7

-find relationship
twice as slow
Why - Rate is directly proportional

Question 8

What is the variable in this experiment?

Answer 8

Temperature

Question 9

Why is a dilute solution of sodium thiosulfate used in this experiment?

Answer 9

So that measured times will not be too short at higher temperatures (since r.or increases at higher temperature and if a concentrated solution were used, the reaction would proceed too fast to get a result)

Question 10

Why is the temperature taken after the HCl is added?

Answer 10

Some cooling may have occured on addition of the HCl

Question 11

Why is a stop-clock used in this experiment?

Answer 11

To accurately measure the time taken to obscure the cross

Question 12

The graph for temperature versus rate is a curve, unlike the linear graph for concentration versus rate. Why is this so?

Answer 12

Rate of reaction is not directly proportional to the temperature

Question 13

Give two everyday examples of temperature affecting the rate of reaction

Answer 13

• Food being stored in a fridge. The cold temperatures slows down the rate of decomposition of the food
• Catalytic converters in a car work most efficiently when heated as the rates of various reactions in catalytic converted are increased at higher temperatures

Question 14

Name the gas given off when sodium thiosulfate reacts with HCl in this experiment and describe the smell

Answer 14

Sulfur dioxide - irritating and strong smell