C5 - Energy Changes Flashcards
What is energy moved around in
Chemical equations
Chemicals store a…
Certain amount of energy
Different chemicals store different amounts
What happens if a product of a reaction stored more energy than the reactants
Products must have taken in the difference in energy between the products and reactants from surroundings during reaction
What happens if the products store less energy than the reactants
The excess energy was transferred to the surroundings
What is conserved during chemical reactions
Energy
as overall energy doesn’t change
What happens in exothermic reactions
Heat is given out to surroundings - rise in temp
Transfers energy to surroundings
E.g combustion - gives out lots of energy
Neutralisation reactions are ectothermic
Many oxidation reactions are exothermic
Some hand warmers exothermic - Oxidation of iron in air
What Happens in endothermic reactions
Energy is taken in from surroundings - fall in temperature
Reaction between citric acid and sodium hydrogencarbonate is endothermic
Thermal decomposition - heating calcium carbonate causes it do decompose into calcium oxide and carbon dioxide
Sports injury packets - instant cool
What are reaction profiles
Diagrams that show the relative energies of the reactants and products in a reaction, and how the energy changes over the reaction course
Exothermic reaction profile
Reactants start with more energy than products as energy is released
Initial rise in energy represents activation energy
What is the activation energy
Minimum energy required for reactants to collide and react with each other
Greater activation energy = larger energy needed to start reaction
Reaction profile of an endothermic reaction
Reactants energy starts lower than products as energy is taken in
Difference in height represents overall energy change during reaction per mole
Still an activation energy above the products energy required for reaction
What is needed to break bonds
A supply of energy
What happens during a chemical reaction
Old bonds are broken and new ones are formed
Energy supplied to break existing bonds - endothermic
Energy released to form new bonds - exothermic
Energy amount during exothermic reaction of bonds
The energy released to form the bonds is greater than the energy used to make
Energy amount during the endothermic reaction of bonds
Energy used to break bonds is greater than the energy released to make bonds
