The rate and extent of chemical changes

Rates of reaction:

The rate of a chemical reaction is how fast the reactants are changed into products. A slow reaction is chemical weathering e.g. acid rain damage to limestone buildings. A moderate speed reaction is magnesium reacting with acid. A fast reaction is burning or explosions. 

Reaction speed can be measured using a graph and, usually, the steeper the line, the faster the reaction.

The collision theory is that the rate of a chemical reaction depends on 1) collision frequency of reacting particles. The more collisions that happen, the faster the reaction. 2) energy transferred during a collision. Particles have to have enough energy for a collision to occur.

The activation energy is the minimum amount of energy that particles need to react. Particles need this much energy to break the bonds in the reactants to start the reaction. 

Factors affecting rates of reaction:

All these factors increase the number of successful collisions between the reacting particles. 

1) Temperature - when the temperature increases, the particles have more energy to move faster and if they move faster, they can collide more frequently. So increasing the temperature, increases the rate of reaction.

2) Concentration or pressure - high concentration or pressure means more particles are in the same volume or space. This makes collisions more frequent so increasing the concentration/pressure, increases the rate of reaction.

3) Surface area - increasing the surface area to volume ratio means the same volume of the solid, the particles have more area to work on so there are frequent collisions. So increasing surface area, increases the rate of reaction.

4) Catalyst - a catalyst is a substance that speeds up a reaction without being used up. They decrease the activation energy, making an alternative reaction pathway. This makes the particles have more energy for colliding so presence of a catalyst increases the rate of reaction.

Practicals measuring rate of reaction:

Rate of reaction = amount of reactant used or amount of product formed/time.

Precipitation and colour change: This is recording a visual change, this is used when an initial solution is transparent and the product of the reaction is a precipiate which clouds the solution. The quicker the turbidity changes (cloudiness changes) the quicker the reaction. But this practical is subjective because some may say the turbidity changes quicker than others. 

Change in mass: This is measuring the speed that a reaction produces a gas. You need a mass balance and take regular intervals of time to record the reading on the balance. The bigger/faster the decrease in mass, the quicker the reaction. But it releases gas straight into the room.

Volume of a gas: This involves a gas syringe to measure the gas given off. The more gas given off in a given time, the quicker the reaction. If…