Measuring rates of reaction
There are different ways to determine the rate of a reaction. The method chosen usually depends on the A substance that reacts together with another substance to form products during a chemical reaction. and A substance formed in a chemical reaction. involved, and how easy it is to measure changes in them.
In addition, how long a reaction is observed for depends on the rate of reaction. Reactions can vary from being almost instantaneous to taking years to complete. In the lab, reactions are usually followed over a few seconds or minutes.
Question
A corrosion process in which iron or steel reacts with oxygen and water. is a slow reaction. Give four examples of a very fast reaction.
The process of burning by heat., explosions, The reaction between an acid and a base to form a salt plus water. reactions and A reaction in which an insoluble solid is formed when certain solutions are mixed. are very fast reactions.
Measuring mass
The change in The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of a reactant or product can be followed during a reaction. This method is useful when carbon dioxide is a product which leaves the reaction container. It is not suitable for hydrogen and other gases with a small The sum of the relative atomic masses of the atoms in a chemical formula., Mr. The units for rate are usually g/s or g/min.
Measuring volume
The change in The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml. of a reactant or product can be followed during a reaction. This method is useful when a gas leaves the reaction container. The volume of a gas is measured using a gas syringe, or an upside down Long glass tube with a tap and marked with volume measurements, used in titrations.. An upturned measuring cylinder can also be used but this is less When the value of a measurement is close to the true value.. The units for rate are usually cm3/s or cm3/min.
Measuring colour change or formation of a precipitate - Higher
A few reactions produce a colour change, for example due to the production of iodine. A colorimeter measures colour change.
The formation of a A suspension of particles in a liquid formed when a dissolved substance reacts to form an insoluble substance, eg in a precipitation reaction. causes the reacting mixture to change from transparent to Not transparent or see-through.. The rate of reaction can be measured by timing how long it takes for a cross (drawn on a white tile) to disappear.
Graphs
The rate of reaction can be analysed by plotting a graph of mass or volume of product formed against time. The graph shows this for two reactions.
- the horizontal line shows that no more product is being made - the reaction has finished
- rate of reaction does not affect the mass of product formed
The Another word for steepness. On a graph, the gradient is defined as being the change in the 'y' value divided by the change in the 'x' value. It defines how steep a line is. or steepness of the line is equal to the rate of reaction:
- the steeper the line, the greater the rate of reaction
- fast reactions finish sooner (when the line becomes horizontal) than slow reactions