Rate of reaction 1; Reaction times and rates

Some reactions are fast and some are slow.
1. Rusting is slow reaction.
2. burning/explosions are fast reactions
measuring the product formed depends on weather it is solid or gaseous.
1. solids are measured in Grams
2. gasses are measured in cm3
3. The period may be chosen upon the rate of reaction. if it is a slow reaction then g/min or if it is a fast reaction it should be cm3/s.
The volume of gas is usually measured in a gas syringe.
In a typical rates experiment, the mass or volume of product is measured at regular time intervals. It is usual to record these results in a suitable table
1. The results show that the reaction had finished by 4 minutes, as no more gas was produced after that
  1. The mean rate of reaction = 50 ÷ 4 = 12.5 cm3/min
2. However, the rate decreases during the reaction. The analysis below shows how.
The rate of reaction can be analysed by plotting a graph of amount of product against time. The graph below shows this for two reactions
1. Compared to the slow reaction, the graph line for the faster reaction: Has a steeper gradient at the start and becomes horizontal sooner (showing that the reaction time is less)
limiting reactants
1. A reaction stops when all the particles of one of the reactants are used up. In a reaction involving two reactants
  1. The limiting reactant is the one that is all used up at the end of the reaction
2. The reactant in excess is still there at the end of the reaction (although in a smaller amount than at the start)
3. For example, magnesium reacts with hydrochloric acid; Magnesium is the limiting reactant if it is all gone at the end OR hydrochloric acid is the limiting reactant if some magnesium is left at the end
4. reactions happen when particles collide with enough energy. The more reactant particles there are to begin with, the more can be formed. this is why the limiting factor is directly proportional to the product formed.
The amount of product formed in a reaction is directly proportional to the amount of limiting reactant used
1. This means that a graph showing amount of product formed against amount of limiting reactant will give a line that is straight, has a positive gradient & passes through the origin (0,0)
The rate of reaction can be calculated from the gradient of a graph of amount of product against time of reaction
1. 1.) Draw a tangent to the curve (a straight line that represents the gradient at that point)
  1. 2.) Draw a vertical line and horizontal line to form a right-angled triangle with the line from step 1
    1. 3.) Read off the change in amount of product (the vertical line in your triangle)
      1. 4.) Read off the change in time (the horizontal line in your triangle)
        5.) Calculate the gradient. This will be the answer from step 3 divided by answer from step 4
2. In the example; rate of reaction = 10.4 ÷ 2 = 5.2 g/min

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Rate of reaction 1; Reaction times and rates

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	Created by andrewstalker about 10 years ago