Topic 7 - rates of reaction and energy changes / SC18+19 Flashcards
what is meant by Rate of reaction
the speed at which reactants are turned to porducts
what are ways to determine the rate in a reaction ( practical)
measuring the amount of gas produced
how fast the colour of the liquid changes
How do reactions occur in regards to particles
- particles collide with each other
the collisions must have enough activation energy
what is activation energy
the minimum energy needed by reactant particles for a reaction to happen
what does more energy result in
- more successful collisions
- faster reaction
how does temperature effect the rate of reaction
- rate of reaction increases as temperature increases
- the particles gains energy
- particles move faster
- the frequency of collisions increases so higher proportion of successful collision
how does concentration effect the rate of reaction
- increased concentration, increases the rate of reaction
- there are more particles in the same volume
the frequency of successful collisions increases
how does surface are to volume ratio effect the rate of reaction
eg when lumps are made into powder
- increased surface area increased rate of reaction
- more particles of reactants available to react.
the frequency of successful collisions increases
what is a catalyst and what does it do
- often transition metals
- substances that speed up the rate of reaction.
- they remain unchanged chemically or unchanged by mass
- they provide alternative reaction pathways with a lower activation energy
how does a catalyst increase the rate of reaction
- they provide alternative reaction pathways with a lower activation energy
- so less energy is needed per collision for a reaction to occur
exothermic or endothermic?
neutralisation reaction
displacement reactions
precipitation reaction
neutralisation - always exothermic
displacement - always exothermic
precipitation - can be exothermic or endothermic
what is meant by exothermic
energy is transferred from stores of energy in a chemical reaction to the surroundings
what is meant by endothermic
energy is transferred from surroundings to stores of energy in a reaction
what does exothermic and endothermic reactions do to bonds
endothermic reaction break bonds
exothermic reaction make bonds
describe the overall heat change in an exothermic reaction
the reaction is exothermic if there is more heat released when forming the bonds in the product than is required in breaking bonds in the reactant
- the overall energy change decreases
- due to heat being taken from the surroundings to the reaction
