Kinetics Flashcards
What is activation energy?
The minimum energy needed for a reaction to occur
What is a catalyst?
A substance that speeds up a chemical reaction but is chemically unchanged at the end. They work by providing an alternate reaction pathway with a lower activation energy
What is enthalpy change?
A heat change at constant pressure
What is the rate of a reaction?
Change in the concentration of a reactant (or product) per unit time
How do you calculate the rate of reaction?
Amount of product/ Time
What are 3 methods for measuring the rate of reaction?
- measuring a decrease in mass
- measuring the volume of gas given off
- timing how long it takes for a precipitate to form
What does collision theory state?
For a reaction to occur, particles must:
-Collide with each other
-Have the correct orientation
-Have sufficient energy to react (activation energy)
What 3 things can cause the rate of reaction to increase?
-Increase the frequency of collisions
-Increase energy of reactants
-Lower the activation energy using a catalyst
How do you increase the rate of reaction?
-Increasing the concentration
-Increase the surface area
- Increase temperature
- Add a catalyst
-Increasing the pressure
How does increasing the concentration/pressure increase the rate of reaction?
-Increases the number of reactant molecules per unit volume of a solution
-Increases the frequency of collisions
How does increasing the surface area increase the rate of reaction?
- More reactant is exposed
- More successful collisions
How does increasing the temperature increase the rate of reaction?
- Increases the kinetic energy of reactant molecules
- More have sufficient energy to react and so there are more successful collisions
How does adding a catalyst increase the rate of reaction?
- Lowers activation energy
- More particles have sufficient energy to react
What does a Maxwell- Boltzmann distribution curve look like?
What does the starting point of a Maxwell- Boltzmann distribution curve show?
Only very few reactant molecules have a low amount of energy
What does the end of a Maxwell- Boltzmann distribution curve show?
Only very few reactant molecules have a high amount of energy
Where does the modal/ most probable amount of energy lie on a Maxwell- Boltzmann distribution curve?
At the very peak of the curve
Where does the mean average particles with energy lie on a Maxwell- Boltzmann distribution curve?
Just below the peak of the curve
What does the area under a Maxwell- Boltzmann distribution curve show?
The total number of reactant particles
Does the Maxwell-Boltzmann distribution curve ever touch the x axis and why/why not?
NO because we can’t say theres a maximum amount of energy particles have as it goes to infinite
Which part of a Maxwell- Boltzmann distribution curve shows the particles that have sufficient energy to react?
Area shaded in purple
What are you increasing if you increase the concentration in a reaction?
Increasing the number of particles present
What happens to a Maxwell- Boltzmann distribution curve if you increase the concentration?
The curve shifts upwards as area is increased due to increased number of particles
What stays the same although the concentration is increased in a reaction?
The proportion of molecules that can react
What happens to a Maxwell- Boltzmann distribution curve if you increase the temperature?
The curve shifts down and to the right as the mode and mean shift to the right. Increases the kinetic energy of particles so increases the frequency of collisions and the number of particles with sufficient energy to react
Does the area under the Maxwell Distribution curve change when the temperature is increased?
NO. You’ve just changed the proportion of molecules that have sufficient energy to react
What happens to a Maxwell- Boltzmann distribution curve if you add a catalyst?
The activation energy line shifts to the left as catalysts lower the activation energy. A larger number of particles now have sufficient energy to react. More successful collisions.
What does an exothermic and endothermic reaction profile look like?
What does an exothermic reaction profiles with a catalyst look like?
What does an endothermic reaction profiles with a catalyst look like?
What are the two types of catalysts?
- Homogenous
- Hetrogenous
What is a homogenous catalyst?
Catalyst in the same state/ phase as the reactants
What is a heterogeneous catalyst?
Catalyst in a different state/ phase to the reactants
What are the benefits of having a catalyst?
Increases rate at lower temperatures and pressures. Therefore less energy needed. Therefore less economic and environmental cost.
Why does the Maxwell-Distribution curve go through the origin?
No particles have no energy
For the reaction A (g) —–> B (g) + C (g) explain why, even though most molecules have lower energy than the activation energy for decomposition to occur, most of A will eventually decompose.
Molecules will gain energy due to collisions and, therefore, there will always be some molecules with more energy than activation energy.
Why does a small increase in temperature lead to a large increase in rate of reaction?
-Area under the curve beyond Ea is larger
-Many more molecules have energy greater than or equal to the activation energy
-Large increase in the frequency of successful collisions
What is the effect on the rate of reaction if the volume of a container is halved?
-If volume decreases, pressure increases
-Higher pressure means more particles per unit volume
-More successful collisions per second
-Increased rate of reaction
Why are catalysts often used in powder form or coated on a mesh?
To increase the surface area
What is uncertainty?
An estimate attached to a measurement which characterizes the range of values within which the true value lies
What is experimental error?
The difference between a measurement and the true value or between two measured values.
What is precision?
When measurements are close together
What is accuracy?
When measurements are close to the correct value
