Topic C5- Energy Changes Flashcards
What must have happened if the products of a reaction stored more energy than the original reactants
They must have taken in the difference in energy between the Products and reactants from the surrounding during the reaction
What must have happened if the products of a reaction stored less energy than the original reactants
Then the XS energy was transferred to the surroundings during the reaction
What is an exothermic reaction
Is one which transfers energy to the surroundings usually by heating
This is shown by a rise in temperature
Is the best example of an exothermic reaction
Burning fuels also called combustion
Neutralisation reaction
What are the every day uses of exothermic reactions
Some handwarmers use the exothermic oxidisation of iron in the air to release energy
Self heating cans of hot chocolate and coffee also rely on exothermic reaction between chemicals in their bases
What are endothermic reactions
Ones which takes in energy from the surroundings
This is shown by a fall in temperature
What examples of endothermic reactions
Thermal decomposition
What is a day-to-day use of endothermic reactions
Are used in some sports injury packs the chemicals react allows the pack to become instantly cooler
What are reaction profiles
Are diagrams that showed the relative energy of the reaction and products in a reaction, and how the energy changes over the course of the reaction
How is an exothermic reaction shown on a reaction profile
The products are at a lower energy than the reactants.
The difference in height represents the overall energy change in the reactions
The initial rise in energy represents the energy needed to start the reaction this is the activation energy
The activation energy is the minimum amount of energy that reactants need to collide with each other and react. The greater the activation energy and more energy needed to start the reaction this has to be supplied
How is an endothermic reaction shown on a reaction profile
The products are at a higher energy than the reactants
The difference in height represents the overall energy change in the reactions
The initial rise in energy represents the energy needed to start the reaction this is the activation energy
The activation energy is the minimum amount of energy that reactants need to collide with each other and react. The greater the activation energy and more energy needed to start the reaction this has to be supplied
What happens during a chemical reaction
Old bonds are broken and new ones are made
What process is bond breaking
Is an endothermic process because energy must be supplied to break existing bonds
What process is bond formation
This is an exothermic process because Energy is released when new bonds are formed
What causes an reaction to be exothermic
The energy released for forming bonds is greater than the energy needed to break them
