Chapter 7

A physical change affects the forces between particles, however the particles and their chemical properties remain the same. Also being reversible. While chemical changes change the particles themselves. For example, forming OH from H2O. Chemical changes include colour change, odour, effervescence and temperature change (from energy being taken in or out).

concentration increases; rate of reaction increases particle size increases; rate of reaction decreases temperature increases; rate of reaction increases catalysts present; rate of reaction increases

a high concentration increases the chance for more successful collisions as there are a lot more reacting particles in the same volume.

a high temperature means that the particles would have more energy (than the activation energy required) and therefore there are more successful collisions. Including more collisions as the particles have more kinetic energy.

the smaller the particle size, the more surface area is exposed. This allows more particles to be in contact with the other particles and therefore more successful collisions are possible.

catalysts increase the rate of reaction as they provide a collision with lower activation energy required, therefore there are more successful collisions as not as much activation energy is required.

the effect of particle size can sometimes be dangerous. If a powdered substance ignites in the presence of air, it can cause an explosion. Explosions are caused by the large surface area of the particles and the very fast rate of combustion. For methane, it can be found in high concentrations in caves. It can be proven to be highly flammable.

You have to determine how much of the gas product is produced (using a gas syringe or cylinder in a trough of water) over a certain period of time and divide it by that. That will give your rate of reaction, of which should have the unit cm^3/s.

add a black cross below a beaker containing one reactant, add the other reactant and record the time it takes for the cross to disappear.

The mass of the reactants would decrease. Therefore, you do so by measuring the mass of reactants on a digital balance at regular time intervals.

reactions initiated by light

as light intensity increase, so does the rate of photochemical reactions

Silver chloride is light sensitive and breaks down to form silver metal with is black (reduction). the more intense the light is on the film, the faster the rate of reaction so a darker photo appears.

the reaction between carbon dioxide and water in the presence of chlorophyll and sunlight (energy) to produce glucose and oxygen

Gain of oxygen

Loss of oxygen

the transfer of electrons from two elements, involving both a reduction and oxidation reaction

When the oxidation states change for an element

purple and turns colourless

colourless to brown

a substance which oxidises another substance during a redox reaction

a substance which reduces another substance during a redox reaction.

Anhydrous cobalt (II) chloride + water ----> hydrated cobalt (II) chloride [blue to pink] Add water for the products to form and heat it up (to evaporate water) for the reactants to form.

A system in a steady state since forward reaction and backward reaction occur at the same rate