rate of reaction ==general concept

What is ?What is ?

Effective collision?Effective collision?

Collision theory?Collision theory?

Factors affecting?Factors affecting?

Activation energy?Activation energy?

Energy level diagram?Energy level diagram?

Rate of reactionRate of reaction

What is the rate of a reaction

The rate of the reaction is how quickly the reaction happens.

Fast reaction

Slow reaction

Iron rusting - a CHEMICAL REACTION with a slow reaction rate.

Wood burning - a CHEMICAL REACTION with a fast reaction rate.

What is ?What is ?







"You can’t react if you don’t collide."

collision theory

1. the molecules must collide to react.

If two molecules simply collide, however, they will not always react; therefore, the occurrence of a collision is not enough.

3 necessary requirements in order for a reaction to take place:

This is the idea of a transition state; if two slow molecules collide, they might

bounce off one another because they do not contain enough energy to reach the energy of activation and overcome the

transition state (the highest energy point).

2. there must be enough energy (energy of activation) for the two molecules to react.

For the reaction to occur between two colliding molecules, they must collide in the correct orientation, and possess a certain,

minimum, amount of energy.

3. the molecules must be oriented with respect to each other correctly.

•If the colliding particles have less than this minimum energythen they just bounce off each other and no reaction occurs.This minimum energy is called the activation energy.

collision theory

•There is a minimum amount of energywhich colliding particles need in order to react

• chemical reaction only occur between particleswhen they collide

What is ?What is ?







Prevent Effective collision

Camera to detect fast moving traffic

Reactants moving too slowly

Molecules bounce ( no reaction)

NO3(gas) + CO(gas) NO2(gas) + CO2(gas)

NOT Effective collision

NO3(gas) + CO(gas) NO2(gas) + CO2(gas)

Reactants not facing right way

Molecules bounce ( no reaction)

NOT Effective collision

Reactants energy is high & oriented right way

Reaction happens

Effective collision

The orientation of collision

Effective collision

Effective collision

Effective collision

Which collision is effective?

What is ?What is ?







•The energy that must be overcome in order for a chemical reaction to occur

•Activation energy is the minimum energy necessary for a specific chemical reaction to occur

•For chemical reaction to have noticeable rate, there should be noticeable number of molecules with the energy equal or greater than the activation energy.

Activation energy

The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner

Activation energy

A little activation energy is added with the aid of a weed burner...

What is activation energy

Not enough kinetic energy for reactants to leap over reaction barrier.

A "hot" reaction in progress showing reactants leaping over the activation energy barrier


Activation energy

Only collisions with enough energy react to form products. The critical amount of energy to make the reaction proceed


A + B C + Dreactants products


activation energy


reactants

products

Activation energy


reactants

productsActivation energy


reactants

products

What is ?What is ?







What affects the rate of a reaction?

Size of reactant

Concentration of reactants

/pressure

Temperature of reaction mixture

catalyst

1. The effect of particle size




•Reducing the size of particles

•increases the surface area

•increases the number of collisions per second.

•Increase the rate of reaction.

•Increase the number of effective collisions.

Increasing the Surface Area of a Solid.

A solid in a solution can only react when particles collide with the surface.The bigger the area of the solid surface,the more particles can collide with it per secondA powder has the largest surface area and will have the fastest reaction rate.

THE EFFECT OF SURFACE AREA ON REACTION RATES

a reaction between magnesium metal and a dilute acid like hydrochloric acid.

Increasing the number of collisions per second increases the rate of reaction.

THE EFFECT OF SURFACE AREA ON REACTION RATES

Magnesium metal


2. Temperature

Increasing temperature will increase energy in the particles leads to an increased probability of favourable collisions.


1. The effect of temperature

•Increase the temperature

•increases the kinetic energy of particles

•Increases the number of collisions per second.



3. Concentration and Pressure

Increasing concentration or pressure increases the rate of a reaction, because the particles are closer together and have an increased probability of favourable collisions.


THE EFFECT OF CONCENTRATION ON REACTION RATES


1. The effect of concentration

•Increase the concentration

•increases the no of particles/unit volume




THE EFFECT OF PRESSURE ON REACTION RATES


1. The effect of pressure in gas

•Increase the pressure of gas

•increases the no of particles/unit volume




4. Catalyst

Often a catalyst is there to provide a favourable surface for a reaction to take place


The black object represents the catalyst

- A catalyst will change the rate of a reaction.- The catalyst itself does not take part in the reaction - It is not changed by the reaction- it is not used up during the reaction.- A catalyst is usually a transition metal, a transition metal oxide

Properties of Catalysts

Examples CATALYSTS ON REACTION RATES

Reaction catalyst

Decomposition of hydrogen peroxide

Manganese (IV) oxide, MnO2

Manufacture of ammonia by the Haber Process

Iron

Contact Process to make sulphuric acid

Vanadium (V) oxide, V2O5


1. The effect of catalyst

•Catalyst provides alternative route

•That has a lower activation energy


•So more particles have energy equal or greater than activation energy.

•Number of effective collisions increase.

4. Catalyst

How does a catalyst work?1) A catalyst provides a surface on which the reaction can take place. This increases the number of collisions between the particles of the substances that are reacting.


How does a catalyst work?

4. Catalyst

How does a catalyst work?2) A catalyst lowers the activation energy This means that the particles can react with less energy than they needed before the catalyst was added. (Think about it: if the government lowered the legal age to buy cigarettes, then more people could legally buy cigarettes. Similarly, if we lower the amount of energy needed for particles to react, then more particles can react).


A catalyst provides an alternative route for the reaction. That alternative route has a lower activation energy.

Activation energy

Activation energy

Activation energy with no catalyst

Activation energy with catalyst

What is ?What is ?







In an exothermic reaction, reactants have a higher energy level than the products.

Energy level diagram

In endothermic reactions the reactants have a lower energy level than the products.

Energy level diagram

End of slides

rate of reaction ==general concept

Education

minimum energy

kinetic energy

aminimumamount of energy

theactivation energy

hot reaction

howquicklythe reaction

therate of reaction

energy level diagram