M3 Chapter 10 - Reaction rates and equilibrium Flashcards
(33 cards)
What is the equation used to calculate rate?
Rate = change in conc / time
What is the unit for rate of reaction?
moldm-3s-1
What must particles do to react?
Collide with sufficient energy (activation energy) and the correct orientation.
Do most collisions result in a reaction?
No
What are the factors affecting rate of reaction?
Temperature
Pressure
Concentration
Surface Area
Catalyst
What is the effect of increasing temperature on rate of reaction? Why?
Increase in temperature increases the rate of reaction.
Because a higher proportion of particles have energy greater than the activation energy meaning more successful collisions per second. Hence, increased rate.
What is the effect of increasing concentration/pressure on rate of reaction and why?
Increased conc/pressure = increased rate of reaction.
Because more particles in given volume hence more frequent successful collisions. Meaning increased rate.
What are the variables in an experiment that can be monitored to calculate the rate of reaction?
Conc of reactant or product
Gas volume of products
Mass of substances formed
How to calculate rate from a conc-time graph?
Draw tangent
Work out gradient
What is a catalyst?
A substance increasing rate of reaction without being used up in reaction.
How do catalysts work and how do they increase the rate of reaction?
They provide an alternative reaction pathway (with lower activation energy)
Due to lower activation energy, more particles have more energy than the activation energy, so more frequent successful collisions, so increased rate.
What does homogenous catalyst mean?
A catalyst remaining in the same phase as the reactants.
Eg: liquid catalyst mixed with liquid reactants.
What does heterogenous catalyst mean?
Catalyst used in the reaction is in different phase to the reactants
Eg: gaseous reactants passed over solid catalyst.
What are catalytic converters?
They are present in vehicles to reduce toxic emission and prevent photochemical smog.
Define activation energy.
Minimum energy that particles must collide with for a reaction to occur.
Name some important features of Boltzmann Distribution.
Area under curve = total number of molecules
Area under curve does not change when conditions change.
Curve starts at origin
Curve does not touch energy axis
Only the molecules with greater activation energy can react
What are the axis in a Boltzmann Distribution?
X axis = energy
Y axis = number of molecules with a given energy
Boltzmann Distribution labelled diagram.
Includes:
Most probable energy
Mean energy
Activation Energy
Draw a labelled Boltzmann Curve showing the effect of catalyst of rate of reaction.
Labelled Boltzmann Distribution curve but with Ea and Ec on the X axis. Should show that the activation energy has decreased.
What does dynamic equilibrium mean?
Occurs when 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? (3)
Conc of reactants/products
Pressure
Temperature
Explain Le Chatelier’s Principle.
If a system at equilibrium is disturbed then the equilibrium moves in the direction that tends towards the disturbance.
CH4(g) + H2O (g) <–> CO (g) + 3H2 (g)
ΔH = +210kJ mol-1.
What effect would increasing the temperature have on the position of equilibrium?
Equilibrium shifts right.
This is because the forward reaction is endothermic. Hence, the yield of Hydrogen increases.
CH4(g) + H2O (g) <–> CO (g) + 3H2 (g)
ΔH = +210kJ mol-1.
What effect would increasing the pressure have on the position of equilibrium?
Equilibrium shifts left.
This is because forward reaction produces more moles of gas than the reverse reaction. Therefore, to combat increased pressure, system shifts to side with less gaseous mol. Therefore, yield of H2 here decreases.
