OCR A-level Chemistry - rates of reaction

What is a successful collision

The reactants colliding with the minimum activation energy required to form the product

What effect does increasing the concentration have on the rate of reaction

It increases the rate of reaction because there are more reactant molecules power unit volume that have the potential to collide successfully with the minimum activation and the correct orientation

What effect does increasing pressure have on the rate of reaction

It increases the rate of reaction because the same amount of molecules occupy a decreased surface area so the concentration increases, this increases the frequency of successful collisions as there is a greater chance of the molecules colliding with the correct orientation and activation energy

How can you follow the progress of a reaction

You can monitor the decrease in concentration of a product/the increase in concentration of a product

How can we measure the production of a gas

Using an inverted measuring cylinder/gas syringe/buirette

What are the 5 factors that affect the rate of reaction

Concentration of reactants, temperature, pressure, surface area of reactants, catalysts

What is steric hinderance

The idea that molecules must collide at the correct orientation for a successful collision to occur

What is a catalyst

A substance that changes the rate of a chemical reaction without undergoing any permanent changes

How does a catalyst increase the rate of a reaction

It provides an alternative reaction pathway with a lower activation energy

What are the two types of catalysts

Homogenous and heterogenous

What is a homogenous catalyst

A catalyst that has the same physical state as the reactants

How do homogenous catalysts work

They react with the reactant to form an intermediate which then breaks down to produce the product and regenerate the catalyst

What is a heterogenous catalyst

A catalyst that has a different physical state from the reactants

How does a heterogenous catalyst increase the rate of reaction

The reactant molecules diffuse to the surface of the catalyst and are absorbed, the reaction then takes place, the product molecules leave the catalyst by desorption and diffuse away from the surface of the catalyst

Why are catalysts used in reactions

They reduce the fuel and energy consumption and therefore reduce the costs of a reaction

Why does a Boltzmann distribution curve start at the origin

To demonstrate that there are no particles with no energy

What does the area under the curve of a Boltzmann distribution curve show

The number of molecules

Why does the curve on a Boltzmann distribution curve not meet the x axis

To show that there is no cap on the maximum energy of a particle

What happens to the curve on a Boltzmann distribution curve when temperature increases

The peak is lowered and shifts to the right

What happens to the point of minimum activation energy when a catalyst is added

It shifts to the left

What are the conditions of system in dynamic equilibrium

The rate of the forward reaction is equal to the rate of the backward reaction and the concentration of reactants and products don’t change and the system must be closed

What are le chatelier’s principles

That when a system in equilibrium is subject to an environmental change the system readjusts to minimise the effect of that change

What is the effect of changing the concentration on equilibrium

If there are more products formed the position of equilibrium shifts to the right/if there are more reactants formed then the position of equilibrium shifts to the left

What is the effect of changing temperature on equilibrium

Increasing temperature shifts the position of equilibrium to favour the endothermic reaction/decreasing temperature shifts the position of equilibrium to favour the exothermic reaction

What is the effect of changing pressure on equilibrium

There is only an effect when there are a different number of gaseous molecules on either side of the equation/increasing pressure shifts the position of equilibrium to favour the reaction with fewer gaseous molecules/decreasing pressure shifts the position of equilibrium to favour the reaction with more gaseous molecules

What is the effect of adding on a catalyst on equilibrium

Nothing because a catalyst speeds up the rate of the forwards and backwards reaction equally