C5 - Energy Changes Flashcards
What is an exothermic reaction?
A reaction in which energy is transferred from the system to the surroundings.
This is shown by a rise in temperature.
What are examples of exothermic reactions?
- Combustions reactions (fire)
- Oxidation reactions (adding oxygen)
- Neutralisation
What are the everyday uses of exothermic reactions?
- Handwarmers
- Self heating cans
What is an endothermic reaction?
A reaction in which energy is taken in from the surroundings to the system.
This is shown by a fall in temperature.
What are examples of endothermic reactions?
- Thermal decomposition
- Citric acid + sodium hydrogen carbonate
What are the every day uses of endothermic reactions?
Sports injury packs
How can energy transfer be measured? (Practical)
Look in book
Did this with mr jack smth
- Take temp of reagents
- Mix them in a polystyrene cup
- Measure temp of the solution at the end of the reaction
Energy transfer can be measured
What is a reaction profile?
A diagram that shows the relative energies of the reactants and the products in a reaction, and how the energy changes over the course of the reaction.
Describe the reaction profile of an exothermic reaction
The products are at a lower energy than the reactants
The initial rise in energy represents the activation energy.
Describe the reaction profile of an endothermic reaction
The products are at a higher energy than the reactants.
The difference in height represents the overall energy change during the reaction.
What is activation energy?
Minimum amount of energy required to break the bonds, so a reaction can take place.
Exothermic bond energies
Bond breaking is an exothermic process.
In exothermic reactions the energy released by forming bonds is greater than the energy used to break them.
Endothermic bond energies
Bond forming is an endothermic process.
In endothermic reactions the energy used to break bonds is greater than the energy released by forming them.
What is the equation for overall energy change?
Energy required to break bonds - energy released by forming bonds = the overall energy change
