C8- the rate and extent of chemical change 💥

• the rate of a chemical reaction, is the speed at which a chemical reaction takes place

• the mean rate of reaction can be calculated, by using equation= • quantity of product formed ➗ time taken

• if the quantity of product against time is plotted, the slope of the line gives us an idea of the rate of reaction. • this is because, the sleeper the slope, the faster the reaction

• ; the slope of the line will gradually become less steep- telling is rate of the reaction is decreasing [the reaction is slowing down.] • this is because, a lot of the reactant molecules have already reacted, and turned into product- therefore, fewer reactant molecules are available to react.

• at the end, the slope of the line is now zero, and the line is flat. • this is because, at this point the reaction has stopped, since all of the reactant molecules have already reacted.

• the quantity of product formed is typically in grams • ; if our product is a gas, the quantity is then measured in cm^3

• the rate is initially fast; the reaction then slows down and the reaction finally stops

• collision theory, is a scientific explanation of how chemical reactions occur. • ; collision theory also explains how various factors, can affect the rates of reactions

• collision theory states that: chemical reactions can only occur, when the reacting particles collide with each other. • This is because, the collisions must have sufficient energy • ; collision theory also states, the rate of a chemical reaction, is determined by the frequency of fruitful collisions [successful]

• collision theory states that the reaction between reactants, is due to: the collisions of the reactants particles, and the energy they have when they collide

• not all collisions lead to a reaction because, they have a certain minimum energy known as the activation energy.

• Any change in conditions that increase: the number of collisions, and the number of the particles, will increase the rate of reaction.

• temperature • the concentration of liquids, and pressure of gases. • the surface area of solid reactants • and, the presence or absence of a catalyst

• frequency, is the number of successful collisions, per second

• collision theory states, that the reaction between reactants is due to: the collisions of the particles of the reactants, and the energy they have when they collide is needed • so increasing the surface area, exposes more solid particles to the other reactant • this then increases the frequency of successful collisions [of the reactants’ particles]- and therefore, the rate of reaction increases. • This is because, if surface area increases—> more particles are available to react——> more successful collisions——> and the rate of reaction increases.

• smaller sized blocks of solid reactant, have a greater surface area: volume ratio than larger blocks • meaning that smaller sidled blocks of solid reactant, have more particles on the surface- meaning there are more collisions per second [per unit time] • and, this increases rate of reaction

• the surface area of a solid reactant can be increased, by: • breaking it up into very small pieces, and decreasing the particle size

• the units for rate of reaction, are: g/s , cm^3/s and mol/s

• there can be different units for rate of reaction, depending on whether volume or mass, is being measured • This is because, the mass of a solid product is often measured in grams; the volume of a gaseous product, is often measured in cm^3

• there’s more than one unit, for rate of reaction because: • if a gas was being given off during a reaction, you could: take some measurements, and then work out the volume being given off per second, at any particular time during the reaction. • ; rate usually measured, by looking at how fast the concentration of one of the reactants is falling at any one time.

• many collisions don’t lead to a chemical reaction because: • the particles may not collide with enough energy or in the correct orientation • This is because, the particles need to be moving towards in each other, and facing each other- so they don’t simply bounce off each other, which would result in an unsuccessful collision.

This is because, if surface area increases—> more particles are available to react——> more successful collisions——> and the rate of reaction increases.

• temperature • speed • number of collisions • energy • greater than Ea • chance of successful collisions

• pressure • pushes and squashes • successful collisions