Kinetics Flashcards
What are the 4 factors effecting the rate of reaction?
Temperature
Surface area
Concentration
Presence of a catalyst
What does collision theory state?
Particles must collide for a reaction to happen
What is activation energy?
Particles collide with the correct amount of energy
What is a maxwell Boltzmann distribution?
A plot of the number of molecules with a certain amount of kinetic energy
Curves will only cross each other once
An increase in temperature will increase the number of particles with a higher kinetic energy and so the graph shifts to the right
How can rate be measured?
By:
Consumption of reactants or production of product
What are the two equations that can be used for measuring rate?
Amount of reactant used OR amount of product formed / time
When do chemical reactions happen?
When molecules or particles of reactants collide
These collisions must happen with the correct amount of energy for a reaction to take place which is called activation energy
When does no reaction occur?
If a collision happens without particles having activation energy
Instead they just bounce off eachother
What do faster reactions mean?
A faster rate of collisions or an increase in the amount of energy that the particles have when they collide
What is special about all particles in a reaction mixture?
They all have different amounts of energy
Some have less than activation energy and some have more therefore most collisions don’t result in a reaction
What happens if we increase the amount of collisions in a reaction?
We increase the number of successful reactions and so increase the rate if reaction
What happens if we increase the amount of energy particles have?
More particles have energy that is more than the activation energy
So more of the collisions taking place will result in a chemical reaction and so it speeds up the rate if reaction
How does temperature change the rate if reaction?
Temperature is related to how much kinetic energy particles have
Increasing temp increases energy if particles and so particles are moving faster and with more energy which means a greater frequency of collisions that have more energy
This means a greater proportion of collisions result in chemical reactions
What is the overall impact of temperature on rate of reaction?
Two fold
It increases collisions and energy
How does concentration or pressure change the rate of reaction?
Pressure is for gases and concentration is for liquids
Increasing the concentration means more particles in the same volume and so particles collide more frequently which in turn increases the rate if reaction
How does surface area change the rate if reaction?
This is for when one of the reactants is a solid
Only particles on the surface of the solid are available to react
So if you increase the surface area by breaking the solid into smaller pieces or grinding it into a powder the more particles are available or reaction
This increases frequency of collisions which then increases the rate if reaction
How do catalysts change the rate of reaction?
They lower the activation energy by providing an alternative reaction pathway for the chemical reaction
The number of collisions remains the same but more if these collisions will be successful as more of the collisions will take place with greater than activation energy
So the rate of reaction increases
How is the rate of reaction increased overall?
By increasing the rate of successful collisions
What two things can be altered to change rate?
Energy if the molecules and frequency of collisions
Where is activation energy marked on a maxwell distribution curve?
The area to the right of the activation energy line shows the molecules that will react when they collide
What are some tips when drawing maxwell distribution curves?
Correct labels for the axes
Start from the origin
Make peak clearly defined
Make curve flatten out near x axis
How is a decrease in temperature shown on the graph?
Curve becomes higher and the position is shifted to the left
The peak also becomes narrower
How is an increase in temperature shown on the graph?
Becomes lower in height and the position is shifted to the right
The peak of the curve also becomes wider and broader
What do maxwell distribution plots show in summary?
The number of molecules and energy
What should the curve not do after the origin?
Touch the x axis again
What is collision theory?
Chemical reactions occur when particles of substances collide
For a reaction to occur collisions must have energy greater than or equal to the activation energy of the reaction
Particle orientation must also be correct
Define maxwell Boltzmann distribution
Not all molecules in a substance have the same amount of energy
Their energies are distributed in a pattern called the maxwell Boltzmann distribution
Molecules with energy greater than the activation energy will collide with enough energy to result in a reaction
What are the features of a Maxwell Boltzmann distribution curve?
Mean energy line going up
Most probable energy line also going up
Activation energy line going up
Zero molecules have zero energy shown
X axis= kinetic energy
Y axis=number of molecules
How does changing reaction conditions alter the shape of the curve?
Number of particles with energy greater than the activation energy is different
Total area under the curve represents the total number of molecules in the sample and this must remain constant
What is the effect of temperature on rate of reaction?
When a substance is heated thermal energy is transferred to it
This energy is converted to kinetic energy and the molecules of the substance now move faster and further
Increase movement of the molecules means collisions will occur more often with greater energy
More collisions have energy greater than the activation energy= a reaction
What is the effect of concentration and pressure on he rate of reaction?
When concentration of a sample is increased more molecules of a substance occur in the same volume = packed closer together
Collisions between molecules are more likely + chances of a collision with greater activation energy increases= rate if reaction increases
Increasing pressure has similar effect as molecules are packed closer together into a smaller volume
What is the effects of catalysts on rate of reaction?
A catalyst increases the rate if reaction without being used up in the reaction itself
It works by providing an alternative reaction pathway that requires a lower activation energy for the reaction to occur
Maxwell Boltzmann distribution curve is unchanged in shape but position of activation energy is shifted to the left so a greater proportion of molecules have sufficient energy to react
Explain the effect that lowering the temperature would have on the rate of reaction
Exam question
Lowering the temperature would mean less thermal energy is transferred to a substance
Molecules move slower due to having less kinetic energy
Decreased movement means less collisions will occur less often
Decreasing temperature decreases rate of reaction
How does a decrease in pressure change the rate of reaction?
Amount of gas present has been reduced so the pressure as been reduced
Particles are further apart
Fewer collisions between gas particles so fewer successful collisions
