What happens in an exothermic reaction?
Energy is transferred from the reactants to the surroundings meaning the temperature of the surroundings increases.
What are 3 examples of exothermic reactions?
- Combustion
- Neutralisation
- Some oxidation reactions
What are exothermic reactions used for?
- Hand Warmers
- Self heating cans
What does the reaction profile of an exothermic reaction look like?
The products have less energy than the reactants
What happens in an endothermic reaction?
The reactants take in energy from the surroundings meaning the temperature of the surroundings decreases and the products have increased energy.
What is an example and a use of endothermic reactions?
- Example - Photosynthesis
- Use - Cooling packs
What does the reaction profile for an endothermic reaction look like?
The energy level of the products is greater than that of the reactants.
What is activation energy?
The minimum amount of energy particles must have in order to react
Bond energy calculations.
That’s it. Practice bond calculations 😭
- REMEMBER BREAKING BONDS is endothermic and is positive
- MAKING BONDS is exothermic and negative
What does the temperature changes RP investigate?
The maximum temperature reached by different volumes of sodium hydroxide in a neutralisation reaction between hydrochloric acid and sodium hydroxide.
What are the different variables in this RP?
- Independant - volume of sodium hydroxide solution
- Dependant - max temperature reached
- Control - volume of hydrochloric acid, concentration of both acid and sodium hydroxide
Describe how to do the temperature changes RP (part 1)
- Measure out 30cm3 dilute hydrochloric acid using a measuring cylinder. Transfee the acid into a polystyrene cup and stand it in a beaker to prevent it from falling over.
- Measure the start temperature of the acid and record. Then use the measuring cylinder to measure out 5cm3 of sodium hydroxide solution and add it to the cup.
- Put a plastic lid on the cup and place a thermometer in it, making sure the bulb of the thermometer is in the solution. Use the thermometer to gently stir the solution.
- Carefully watch the rise in temperature until it stops increasing. Record the highest temperature reached.
Describe how to do the temperature changes RP (part 2)
- Rinse and dry out the cup and repeat the experiment multiple times, increasing the volume of sodium hydroxide each time by 5cm3 up to 40cm3.
- Repeat the experimenr again at each value up to 40cm3 and calculate a mean maximum temperature reached at each volume.
- Plot the data on a graph
What should the graph in the temperature change RP show?
As the volume increases, the maximum temperature reached increases as more sodium hydroxide particles are reacting in the acid. As this reaction is exothermic, more energy is released and therefore the maximum temperature increases.
However, at a certain point, the max temperature will begin ti decrease once the acid has become a limiting reactant. This is because the energy released is now spread out onto a greater volume.
Why is a polystyrene cup and a lid used?
The polystyrene cup is used as it is a good thermal insulator so heat loss through the bottom and sides is minimised. A plastic lid is used to minimise heat loss to the air.
