energy changes

Question 1

What makes a reaction exothermic?

Answer 1

Exothermic reactions transfer energy to the surroundings and the
temperature of the surroundings increases

Question 2

What makes a reaction endothermic?

Answer 2

Endothermic reactions take in energy and the temperature of the surroundings decreases

Question 3

Give examples of exothermic reactions

Answer 3

• combustion reactions
• many oxidation reactions
• most neutralisation reactions.

Question 4

Give an everyday use of exothermic reactions

Answer 4

self-heating cans and hand warmers

Question 5

Give examples of endothermic reactions

Answer 5

• thermal decomposition reactions
• the reaction of citric acid and sodium hydrogen carbonate

Question 6

Give an everyday use of endothermic reactions

Answer 6

instant ice packs which can be used to treat sports injuries

Question 7

REQUIRED PRACTICAL: TEMPERATURE CHANGE

Answer 7

Aim: To investigate the variables that affect temperature changes in
reacting solutions.
Context: You could investigate one or more chemical reactions, for example:
* acids reacting with metals, metal carbonates or with alkalis
* displacement reactions of metals.
Method: Reacting two solutions, e.g. acid and alkali
1. Place the polystyrene cup inside the glass beaker for stability.
2. Measure an appropriate volume of each liquid, e.g. 25 cm3
3. Place one of the liquids in a polystyrene cup.
4. Record the temperature of the solution.
5. Add the second solution and record the highest or lowest temperature obtained.
6. Change your independent variable and repeat the experiment. Your independent
variable could be the concentration of one of the reactants, or the type of acid/alkali
being used, or the type of metal/metal carbonate being used.
Analysis: The bigger the temperature change in the reaction, the more energy is
absorbed or released.
Evaluation: The biggest source of error in this experiment is unwanted heat transfer.
Using a lid can help to reduce this.

Question 8

What is the activation energy?

Answer 8

The minimum energy needed by particles when they collide for a
reaction to occur

Question 9

On a reaction profile, where is the activation energy?

Answer 9

The difference between the reactants energy level and the peak of the line

Question 10

What is the difference between an exothermic and endothermic reaction profile?

Answer 10

EXOTHERMIC: Energy level decreases from start to finish. The difference from reactants to products is the energy released

ENDOTHERMIC: Energy level increases from start to finish. The difference from products to reactants is the energy absorbed