rates of reaction

particle theory

All matter is made up of tiny particles, and these particles are in constant motion. Temperature affects the speed of the particles.

collision theory

in order for a chemical reaction to occur, two or more reactant particles must collide with sufficient force (energy) and at the correct orientation.

define reaction rate

A measure of how fast reactants become products during a chemical reaction.

what is activation energy

the minimum amount of energy required for a chemical reaction to proceed.

relate particle theory and collision theory to chemical reactions

All matter is made up of tiny particles which are in constant motion. In order for a chemical reaction to occur, two or more reactant particles must collide with sufficient force and at the correct orientation.

increasing number of particles in a given volume

increases frequency of collisions

decreasing the speed of particles by cooling

decreases frequency of collisions

decreasing number of protons in a given volume

decreases frequency of colliosions

increasing speed of particles by heating

increases frequency of collisions

what are the factors affecting rate of reaction?

temperature, concentration, surface area, catalysts

temperature

if the temperature is raised, it can increases the rate of a chemical reaction. raising temperature causes reactant particles to move more quickly, meaning they have more energy (kinetic). particles that are moving more quickly with more energy have a higher chance of colliding successfully and will collide more often.

i.e. gives more energy

concentration

by increasing the concentration of particles (number of particles) it increases reaction rate. increasing concentration means that more particles are closer together, increasing the chances of collisions.

surface area

increases reaction rate. if a solid reactant is broken into small pieces or grounded into a powder, its surface area has increased. this means more particles are exposed, increasing chances of collisions between particles.

catalysts

they are not part of the reaction, but speed up the reaction. some catalysts provide a specific site for collisions to occur, while others lower the amount of energy required to start a reaction. (activation energy)

what do scientists mean when they talk about rate of reaction

how fast the reaction happens

what are the two ways of measuring rate

1. measuring how quickly the products are made

2. measuring how quickly one of the reactants disappears

what happens if the line is steeper (higher ig…)?

faster rate of reaction

why do reactions start out at a relatively fast rate?

this is when the concentration of the reactants is highest. there is a higher frequency of collisions

why do reactions slow down after a period of time?

concentration of reactants falls, meaning collisions become less frequent.

what does it mean when the line becomes horizontal?

the reaction has stopped

why do reactions eventually stop?

eventually all the reactant particles have reacted, so no more collisions can occur.

how do you speed up the reaction rate?

1. increase concentration (number of reactants)

2. increase temperature

3. increase surface area of reactants

4. add a catalyst

what happens at higher temperatures during chemical reactions?

The number of collisions occurring between reactant particles is greater because the particles are moving quicker. When a collisions occurs, there is more chance of a reaction taking place because the kinetic energy in the particles is greater.

why are collisions less during lower temperatures?

Particles are moving more slowly in lower temperatures. When a collision occurs, there is less chance of a reaction happening because the kinetic energy in the particle is less.

why does the rate of a chemical reaction changes over time?