The Rate And Extent Of Chemical Change Flashcards
Rate of reaction formula
Amount of reactant used / time
Amount of product formed / time
Factors affecting the rate of reaction
Surface area
Temperature
Concentration / pressure
Catalysts
How concentration affects the rate of reaction practical
Using a measuring cylinder, add 50 cm3 of dilute sodium thiosulfate solution to a conical flask
Place the conical flask on a piece of paper with a black cross drawn on it
Using a different measuring cylinder, add 10 cm3 of dilute hydrochloric acid to the conical flask
Immediately swirl the flask to mix its contents, and start a stop clock
When the cross can no longer be seen, record the time on the stop clock
Collision theory - surface area
When more of the surface area is exposed, there are more particles able to react = more collisions, and a faster reaction
Collision theory - temperature
When particles are hotter, they have more energy, making a collision more likely
Collision theory - concentration
The more concentrated the solution is, the faster the reaction
High concentration = more crowded particles, therefore more collisions
Collision theory - pressure
When increasing the pressure we are squeezing the molecules closer together (making them more concentrated) = more collisions
Catalysts
Lowers the activation energy
Reversible reactions
Can go forwards and backwards
If the forward reaction is exothermic, the backward reaction will be endothermic, and vice versa
Same amount of energy is transferred
Dynamic equilibrium
The rate of the forward reaction is the same as the rate of the backward reaction in a closed system
Closed system
Contains a fixed amount of matter
A dynamic equilibrium can only exist within a closed system
The effect of changing conditions on equilibrium
Le Chatelier’s Principle - if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change to re-establish an equilibrium
The effect of changing concentration
If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again
If the concentration of a product is decreased, more reactants will react until equilibrium is reached again
The effect of temperature changes on equilibrium (Exothermic)
If the temperature of a system at equilibrium is increased, products at equilibrium decreases for an exothermic reaction
If the temperature of a system at equilibrium is decreased, products at equilibrium increases for an exothermic reaction
The effect of temperature changes on equilibrium (Endothermic)
If the temperature of a system at equilibrium is increased, products at equilibrium increases for an endothermic reaction
If the temperature of a system at equilibrium is decreased, products at equilibrium decreases for an endothermic reaction
The effect of pressure changes on equilibrium
An increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules
A decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules
