Chapter 10 Reaction Rates and Equilibrium Flashcards
What is the rate of reaction?
Change in concentration of a reactant or a product in a given time.
Measures how fast a reactant is being used up or how fast a product is being formed
How is rate calculated?
rate= change in concentration/time
How does the rate change due to time?
Rate is fastest at the start, as each reactant is at its highest concentration
Rate slows down as the reactants are being used up and their concentration decreases
Once one of the reactants has been completely used up, concentration stops changing and the rate becomes 0
What is the collision theory?
States 2 reacting particles must collide for a reaction to occur
Effective collisions must have correct orientations and must have sufficient energy to overcome the activation energy barrier of the reaction
Increasing concentration increases rate as particles collide more frequently
What is a catalyst?
A substance that changes the rate of a chemical reaction without undergoing permanent change, it is not used up in the chemical reaction
May react with a reactant to form an intermediate or may provide an alternative reaction pathway of lower activation energy
What is a homologous catalyst?
A catalyst that has the same physical state as the reactants. The catalyst reacts with the reactants to form an intermediate then breaks down to give the product and regenrate the catalyst.
What is a heterozygous catalyst?
Has a different physical state from reactants. Reactants are adsorbed onto the surface of the catalyst, where reaction takes place. After the reaction, the product molecules leave the surface of the catalyst by desorption.
What is Boltzmann distribution?
No molecules have 0 energy which curve starts at origin
Area under the curve is equal to a total number of molecules
There is no maximum energy for a molecule - curve does not meet x-axis at high energy
How does temperature affect Boltzmann distribution?
As temperature increases, average energy increases, more molecules have higher energy, graph is stretched over a greater range of energy values, peak of graph is lower and further along the axis, more molecules have energy greater than Ea, greater proportion of collisions
How does catalysts affect Boltzmann distribution?
Provides an alternative route with a lower activation energy, greater proportion of molecules exceed Ea
What are the features of equilibrium?
Rate of forward and backward is equal
Concentration of reactants and products don’t change
Equilibrium systems are dynamic
Must be in closed systems, not affected by outside influences
What is Le Chatelier’s principle?
When a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of the change
How does concentration affect the position of equilibrium?
If there is more products formed, position shifts to the right
If there is more reactants, position of the equilibrium shifts to the left
How does temperature affect the position of equilibrium?
Increase in temperature shifts equilibrium to the endothermic direction
Decrease in temperature shifts equilibrium to the exothermic direction
How does pressure affect the position of equilibrium?
Increase in pressure shifts the equilibrium to the side with fewer particles
Decrease in pressure shifts the equilibrium to the side with more particles
How does catalysts affect the position of equilibrium?
Do not change position of equilibrium, only speeds up rate
How is equilibrium constant calculated?
Kc=[products]^balancing number/ [reactants]^balancing number
What does equilibrium constant show?
The relative proportions of reactants and products in the equilibrium system.
Kc>1, indicates position towards the products
Kc<1, indicates position towards the reactants
