Energy Changes

Question 1

Describe how energy is transferred to or from the surroundings during a chemical reaction

Answer 1

Endothermic - takes in energy from the surroundings

Exothermic - transfers energy out to the surroundings

Question 2

Explain exothermic and endothermic reactions on the basis of the temperature change of the surroundings and give examples of everyday uses

Answer 2

Endothermic - surroundings fall in temperature, thermal decompositions

Exothermic - surroundings rise in temperature, combustion and neutralisation (acid + alkali)

Question 3

Required practical 10: investigate the variables that affect temperature changes in reacting solutions

Answer 3

Method:
Put HCl and sodium hydroxide in separate beakers
Place beakers in 25℃ until they are at the same temperature
Add HCl followed by NaOH to polystyrene cup with lid
Take temperature of mixture every 30 secs and record highest temp
Repeat steps 1-4 with different concentrations of of HCl

Independent -
Dependent -
Control -

Question 4

Describe what the collision theory is and define the term activation energy

Answer 4

Collision theory - For a chemical reaction to occur, the reactant molecules must collide with enough energy

Activation energy - minimum amount of energy needed that reactants need to react

Question 5

HT ONLY: Explain the energy changes in breaking and making bonds and calculate the overall energy change using bond energies

Answer 5

Bond breaking - Endothermic

Bond Forming - Exothermic

Overall = total energy needed - total energy released
energy to break bonds when forming new bond
change