Chemistry- Rates of Reaction

Speed definition

rate of change of difference with time

Rate of reaction definition

change in concentration per unit time of any one reactant or product

formula for average rate of reaction

total volume of oxygen given divided by total time of completion in minutes

average speed formula

total distance over total time

instantaneous rate defintion

rate of reaction at any one point in time of the reaction

initial rate of reaction definition

the rate of the reaction at the beginning

How to find the initial rate of reaction

draw a tangent at point 0,0 

Factors affecting rate of reaction

concentration, pressure, particle size, nature of reactants, temperature and presence of a catalyst

covalent definiton

involve breaking bonds during collisions

ionic solution definition

ions are free to react so usually faster

How does concentration affect rate of reaction

if concentration is increased, more particles, therefore more collisions

How does pressure affect rate of reaction

in gaseous reactions, increasing pressure means decreasing volume, therefore faster

How does particle size affect rate of reaction

if the mass is the same, smaller particles mean more surface area, therefore more effective collisions

How does temperature affect rate of reaction

if reaction is heated, particles gain energy so so more reach activation energy, therefore more effective collisions and also faster collisions (exception of enzymes)

How do catalysts affect rate of reaction

provide an alternative pathway for reactions with different activation energy

pathway definition

a series of steps that take place in a chemical reaction to produce a product

Catalytic poison definition

a substance that makes a catalyst ineffective

What chemicals are in the exhaust fumes of cars?

carbon monoxide (CO), nitrogen monoxide (NO), nitrogen dioxide (NO2) and unburned hydrocarbons

Where does the carbon monoxide come from?

the incomplete combustion of hydrocarbons in the fuel

Where does the NO, and NO2 come from?

the nitrogen gas in the air is oxidised from the engine heat, then reacts with the oxygen 

Why is it important to remove these gases?

Co is poisonous, NO and NO2 are toxic and can form acid rain, unburned bydrocarbons can form photochemical smog

What is a catalytic converter coated in?

platinum (Pt), Palladium (pd) and rhodium (rh)

Reaction that takes place in the catalytic converter

2CO + 2NO = 2CO2 + N2

What happens when a catalyst is poisoned?

the surface area of the catalyst is blocked by a bond between the metal and the poison

What substances act as catalytic poisons

sulfur, phosphourous, plastic silicone compounds, lead

assumptions of the collision theory

for the reaction to occur, the particles must collide with each other, and a collision only results in products if a certain minimum energy is produced in the reaction

Effective collision definition

a collision that results in the formation of products

example of a fast reaction

a firework exploding

example of a slow reaction

a nail rusting

Catalyst definition

a substance that alters the rate of reaction without being consumed in the reaction

what are enzymes

biological catalysts

example of an enzyme

lipidase breaking down lactose in milk

advantages of using catalysts

allows lower temperatures and pressures, lower cost, reduces fossil fuels, reuseable