Topic 5 - Energy Changes

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What is an exothermic reaction
Three examples of exothermic reactions
CombustionNeutralisation reactionsMany oxidation reactions
2 everyday uses of exothermic reactions
Endothermic reaction
Give one example of endothermic reaction
Give one everyday use of endothermic reactions
What is the amount of energy transferred during a reaction proportional to
Proportional to the temperature change of that reaction
How to measure energy transfer in a reaction practical
Temperature in an exothermic reaction
Energy is released and the temperature of the solution will increase
Temperature in an endothermic reaction
Energy will be absorbed and the temperature of the solution will decrease
What is a reaction profile
A reaction profile is a graph that shows how the energy in a reaction changes as the reaction progresses. The graph starts at the energy level of the reactants and ends at the energy level of the producsts. the two points are usually joined by a smooth curve
how to find the overall energy change from a reaction profile graph 
Difference in height between the reactants and products
What is the overall energy change of a reaction
The difference between the energy of the reactants and the energy of the products
Exothermic reaction profile
The reactants have more energy than the products Because energy is released during the reaction
Endothermic reaction profiles
Products have more energy than the reactants Because energy is taken in during the reaction
What is activation energy (Ea )
The minimum amount of energy that reactant particles need when they collide with each other in order to react
How to find activation energy from reaction profile 
difference between where the curve starts and the highest point on the curve
Why are reaction profiles not straight lines 
Some energy is used to break the bonds in the reaactants and start the reactions. the activation energy.
Unit of energy
joules
what type of process is bond breaking
Bond nreaking is an endothermic process because energy must be supplied for bonds to be broken
What process is bond forming
Bond forming is an exothermic process because energy is released when new bonds are formed
What determines if a reaction is exothermic (bonds)
In an exothermic reaction, the total energy released in bond formation is greater than the total energy used in breaking bonds - the leftover energy is released into the surroundings and the temperature rises
What determines if a reaction is endothermic (bonds)
The energy required to break old bonds is greater than the total energy released when new bonds are formed. The extra energy needed is absorbed from the surroundings and the temperature falls
What is bond energy
Bond energy is the amount of energy required to break a particular bond and the amount of energy released when that particular bond is made
A carbon-carbon bond has a bond energy of 348 KJ/mol how much energy is required to break the bonds?
348 KJ of energy is used to break one mole of the bonds
A carbon-carbon bond has a bond energy of 348 KJ/mol how much energy is released when the bonds are formed?
348 KJ of energy is released when one mole of the bonds are formed
How to calculate energy change for a reaction using bond energies 
Draw out the displayed formulas of the molecules in the reactionWork out the amount of energy used in bond breaking by adding up the bond energies of all the bonds in all the reactantsWork out the amount of energy given out from bond making by adding up the bond energies of all the bonds in all the productsthen use the formula to work out the overall energy change
How to work out the amount of energy used in bond breaking in a reaction
Add up the bond energies of all the bonds in the reactants
How to work out the amount of energy used in bond making in a reaction
Add up all the bond energies of the bonds in all of the products
How to find whether a reaction is exothermic or endothermic from its overall energy change
If the overall energy change is negative it is exothermicIf the overall energy change is positive it is endothermic
What is a cell
A cell is a system that contains chemicals which react and produce electricity
Simple cell structure
A cell contains two different electrodes in contact with an electrolyte
Hw does a cell work
What causes a larger voltage produced by the cell?
A large difference in reactivity between the two electrodes
Situation in which the voltage output of a cell will be 0 (electrodes)
No difference in reactivity between the two electrodes because they are the same metal or have the same reactivity
What can cells also be used for
Finding a reactivity order of metals
What is a battery
A battery is formed by connecting two or more cells together in series
Voltage output of a battery
Equals the sum of all of the voltage outputs of the cells it contains
Rechargable cell
The reaction can be reversed by connecting it to an electric current
Why are some cells not rechargable