U1 KA4 - controlling the rate Flashcards
what is meant by collision theory?
for a chemical reaction to occur, the reactant molecules must collide with enough energy
what is the activation energy?
the minimum kinetic energy required for a successful collision to occur
what is meant my collision geometry?
the reactant molecules must be facing the right way for a successful collision to take place, so that the activated complex can be formed
an increase in successful collision causes an increase in…
reaction rate
what are the stages of a reaction?
1 - bonds start to break
2 - activated complex
3 - product molecule forms
describe the first stage in a chemical reaction
as the reactant molecules collide, they must have enough energy to overcome the repulsive forces and start to break the bonds between the atoms
describe the second stage in a chemical reaction
the intermediate stage is reached, in which a high energy, unstable arrangement of atoms is formed called the activated complex
describe the third stage in a chemical reaction
energy is given out as new bonds are formed and the atoms are rearranged into the product molecules
average rate formula
average rate = change in quantity/change in time
relative reaction rate formula
1/t
what apparatus is used to collect soluble gases?
gas syringe
what apparatus is used to monitor the mass lost during a chemical reaction?
a balance
what method is used to collect insoluble gases?
collection over water (downward displacement of water)
factors affecting the rate of a reaction?
temp
concentration
particle size
use of catalyst
describe how increasing temp affects reaction rate
particles have more energy and so move more quickly
increasing the temp increases the rate of the reaction because the particles collide more often
describe how increasing the concentration of reactants affects the reaction rate
more reactant particles moving together
there will be more collisions so the reaction rate is increased
the higher the concentration of reactants the faster the rate of a reaction will be
describe how decreasing the particle size of a reactant affects the reaction rate
surface area is increased so more collisions can take place, increasing the rate of reaction
describe how the use of a catalyst affects the reaction rate
alters the rate of a reaction allowing it to be done at a lower temp + lowers the activation energy
what is an exothermic reaction?
heat is given out
the products will have less energy than the reactants
what is the enthalpy change?
the quantity of energy given out
what is an endothermic reaction?
heat is absorbed
the products will have more energy than the reactants
if a reaction has low activation energy then the reaction rate will be…
fast
if a reaction has high activation energy then the reaction rate will be…
slow
