C10 Reaction Rates And Equilibrium Flashcards
What’s the equation used to calculate rate
Rate = change in concentration/time
What’s the unit for the rate of reaction
mol dm^-3 s^-1
What must particles do in order to react
Collide with sufficient energy (activation energy) and the correct orientation
Do most collisions result in a reaction
No
What are the factors that affect the rate of reaction
Temperature
Pressure
Concentration
Surface area
Catalyst
What’s the effect of increasing temperature on rate of reaction and why
Increasing temp —> increases reaction rate much higher proportion of particles have energy greater than the activation energy —> many more successful collisions per second —> increased rate
What’s the effect of increasing conc/press on reaction rate and why
Increased conc/press —> increased reaction rate
There are more particles in a given vol —> more frequent successful collisions —> increased rate
What are the variables in an experiment that can be monitored to calculate the rate of reaction
Conc of reactant/product
Gas volume of products
Mass of substances formed
How do you calculate rate from a conc time graph
Draw a a tangent
Work out the gradient of the tangent using the equation
Gradient = change in y / change in x
What is a catalyst
A substance which increases the rate of reaction but is not used up in the reaction
How do catalysts work and how do they increase the reaction rate
They provide an alternative reaction pathway (with a lower activation energy)
Due to lower activation energy, more articles have energy > Activation energy, so more freq successful collisions, so increased reaction rate
What does homogeneous catalyst mean
A catalyst that is in the same phase as the reactants
E.g. liquid catalyst mixed with liquid reactants
What does heterogeneous catalyst mean
Catalyst used in the reaction is in different phase to the reactions
E.g. gaseous reactants passed over solid catalyst
What are catalytic convertors
They’re present in vehicles to reduce toxic emission and prevent photochemical smog
Define activation energy
The minimum energy that particles must collide with for a reaction to occur
Name some important features of Boltzmann distribution
Area under the curve = total number of molecules
Area under the curve does not change when conditions alter
The curve starts at the origin
Curve does not touch or cross the energy axis
Only the molecules with energy greater than activation energy can react
What are the axis in a Boltzmann distribution
X axis - energy
Y axis - number of molecules with a given energy
What does dynamic equilibrium mean
It occurs when the rate of forward reaction equals the rate of reverse reaction and concentration of reactants and products remain constant in a closed system
Changing what factors can alter the position of equilibrium
Conc of reactants/products
Pressure
Temperature
Explain the le chateliers principle
If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance
What effect does a catalyst have on equilibrium position
No effect
Because catalyst affects rate of forward and reverse reaction equally
What conditions affects the value of Kc
Temperature
Deduce units for the value of Kc
Mol^-1 dm^-3
What type of system is Kc relevant for
Homogeneous systems in equilibrium
What does Kc being greater than 1 suggest for the equilibrium position
Greater than 1 = over to the right
Less than 1 = over to the left
What effect does decreasing the temp of an endothermic reaction have on Kc
Kc decreases
What effect does increasing temp of an endothermic reaction have on Kc
Kc increase
What effect does decreasing the temp of an exothermic reaction have on Kc
Kc increases
What effect does increasing the temp of an exothermic reaction have on Kc
Kc decreases
