Kinetics I Flashcards
meaning rate of reaction
the change of amount of a reactant or product per unit time
calculation rate of reaction
(amount of reactant used/ product made) / time
State the 2 rules of collision theory
- For a reaction to start, particles must collide in the right orientation
- Particles must have the minimum amount of kinetic energy
meaning activation energy
the minimum amount of energy needed for a reaction to occur by breaking chemical bonds.
The enthalpy difference between the reactant and the transition state.
Describe a maxwell boltzmann distribution graph
- graph starts at 0,0 as no particles have no kinetic energy
- Mode (highest peak): most likely energy of a particle in a sample
- (right of the mode): mean energy the particles have
- Activation energy
Describe how an increased temperature affects rate of reaction
An increased temperature causes an increased rate of reaction. This is because a larger proportion of molecules will have energy greater than the activation energy, thus larger area under the curve beyond the activation energy.
Describe how a decreased temperature affects rate of reaction
A decreased temperature causes a decreased rate of reaction. This is because a smalller proportion of molecules will have energy greater than the activation energy, thus smaller area under the curve beyond the activation energy.
Explain why an increased temperature causes an increased rate of reaction
When the temperature is increased, the average kinetic energy of the molecules increases. This means that more molecules are moving faster and hitting each other with greater energy. Thus, particles collide successfully more often
Describe how pressure changes rate of reaction
Increased pressure causes an increased rate of reaction, but it will not change the maxwell-boltzmann distribution graph.
why does an increased pressure cause an increased rate of reaction
the particles are closer together and collide more often. There are more frequent collisions and a higher chance of reaction
Describe how concentration changes rate of reaction
Increased concentration causes an increased rate of reaction, but it will not change the maxwell-boltzmann distribution graph.
why does an increased pressure cause an increased rate of reaction
the particles are closer together and collide more often. There are more frequent collisions and a higher chance of reaction
Describe how a catalyst changes rate of reaction
the presence of a catalyst causes an increased rate of reaction, but it will not change the maxwell-boltzmann distribution graph, except the activation will move up (to the left)
meaning catalyst
a substance that increases the rate of reaction by providing an alternate pathway that has a lower activation energy. The catalyst is chemically unchanged at the of the reaction
what is the difference between a heterogeneous and homogeneous catalyst
- A heterogeneous catalyst is in a different phase than the reactants. A homogeneous catalyst is in the same phase as the reactants.
- A homogeneous catalyst forms an intermediate species, a heterogeneous catalyst doesn’t.
how does a homogeneous catalyst work
The catalyst lowers the activation energy as it forms an intermediate species by reactants combining with catalyst to form products. The catalyst is reformed again afterwards.
This process includes 2 activation energies
How does a heterogeneous catalyst work
the catalyst lowers the activation energy as it has an increased surface area, which increases rate of reaction because more particles can react with the catalyst at the same time
explain how heterogeneous catalyst works
- Adsorption: The reaction occurs on a solid heterogeneous catalyst. The reactants form weak bonds with the surface of the catalyst
- The bonds in the reactants weaken and break to form radicals. The radicals react with each other to make new substances
- Desorption: The new molecules are released from the surface of the catalyst
what are catalysts used for in industry
- lowering the temperature needed for reactions to occur. This means less energy and cost, and less carbon dioxide produced
- Speeds up the reactions by providing an alternate route for the reaction to occur
- Changes the properties of a product
what are catalysts used for to provide environmental benefits
- Lowers the temperature and pressure required. This reduces the carbon dioxide and energy produces
- Less waste is produced as catalysts allows scientists to use reactions with better atom economies
- Catalytic converters in cars reduce the level of pollution.
