Energy Change Flashcards
Exothermic reaction
One which gives out heat to the surroundings. The energy released is grater than energy used in breaking old bonds.
Endothermic reaction
One which takes in energy from the surroundings. The energy required to break old bonds is greater than the energy released when new bonds are formed.
Energy in chemical reactions
Energy is transferred in chemical reactions because old bonds are broken and new bonds are formed.
Endothermic process
Energy must be supplied to break existing bonds.
Exothermic process
Energy is released when new bonds are formed.
Bond dissociation energy
The energy needed to break the bond between two atoms. Every chemical bond has particular bond energy.
Formula of energy change
Energy change=energy of bond breaking - energy of bond making
Energy change negative
Means that more energy was released in bond making so the reaction is exothermic.
Energy change positive
Means that more more energy was used in bond breaking than was released by bond making do the reaction is endothermic.
Energy level diagram
Shows how the energy in a reaction changes as the reaction progresses.
Catalyst
Is a substance that can speed up a chemical reaction without being changed or used up during the reaction.
Endothermic energy level diagram
Reactants are at lower energy than the products.
Exothermic energy level diagram
Reactants are at a higher energy than the products.
Energy transferred formula
Q = m x c x deltaT
Energy transferred = mass(g) x specific heat capacity x temperature change
Example of an endothermic reaction
- sport injury packs are based on it
- thermal decomposition (it will only break down if it is heated enough)
Examples of exothermic reaction
- fuel combustion
- self-heating coffee
- hand warmer
Disposable hand warmer
- The energy released through oxidation of iron
- iron turns into hydrated iron (lll) oxide, similar to rusting
- sodium oxide is used as a catalyst
How does sports injury pack work?
When ammonium nitrate and water inside the pack mixes, causing an endothermic reaction.
Thermal decomposition example
Decomposition of calcium carbonate. This forms calcium oxide and carbon dioxide when we keep heating the calcium carbonate strongly.
How does catalyst work?
Catalyst provides different pathway so the activation energy is lower. This means that a higher proportion of reactant particles now have enough energy to react when they collide.
ΔH
Enthalpy energy
