To investigate the effect of the concentration of nitric acid on the rate of reaction between the nitric acid and magnesium granules.

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Chukwuweta Ikeh                GCSE CHEMISTRY COURSEWORK

FACTORS AFFECTING RATES OF REACTION

AIM:        

To investigate the effect of the concentration of nitric acid on the rate of reaction between the nitric acid and magnesium granules

BACKGROUND KNOWLEDGE:

The equation for this reaction is:

Word:

Magnesium + Nitric acid                 Magnesium Nitrate + Hydrogen Gas

Balanced Equation:

The products of the reaction between nitric acid and magnesium are magnesium nitrate, water and hydrogen gas.

In my main investigation, I will measure the rate of reaction by calculating the volume of hydrogen gas produced, using a gas syringe, over a certain time period. I will then plot a graph of gas produced against time for all of the different concentrations of nitric acid. Having plotted gas produced against time for each concentration, I will then take a tangent of the line produced by each concentration graph and calculate the rate of reaction for each concentration. The rate of reaction will be calculated as follows:

Rate of reaction = volume of gas produced/time (cm³/second)

Having done that, I will plot a graph of rate of the reaction for each concentration against concentration, and then state what type of relationship there is between the concentration of acid and the rate of reaction. I will then be able to conclude and state from my results what type of relationship my results show as explained on the following page.

I will then analyse and evaluate the data to conclude whether concentration affects the rate of a reaction and how.


Relationships:

Where ‘A’ and ‘B’ are two reactants which react to produce ‘C’ (A+B  C):


RATES OF REACTION:

Rates of reaction are very useful to scientists, especially chemists. Sometimes scientists will discover a reaction from which the products could become very useful and important in industrial production processes, and therefore, it is an advantage if the scientists can speed up such reactions. Equally, scientists can discover reactions whose products are quite harmful and would endeavour to slow down or stop such reactions.

There are many different factors which will affect the rate at which a reaction takes place. In this investigation, I aim to find out which factors affect the rate of reaction (and how) in a specific reaction: the reaction between a metal compound and an acid.

The speed of a reaction can be observed either by: i) how quickly the reactants (the substances which are reacting) are being used up or ii) how quickly products are forming. There are three main methods of measuring the speed of a reaction:

  1. Precipitation

This is when the product of a reaction is a precipitate i.e. it clouds the solution. You can observe a marker through the solution and time how long the marker takes to disappear e.g. use a marker pen to mark a cross (‘X’) on a piece of paper. Assuming the solution is inside a transparent container such as a class beaker or conical flask, place said container on top of the cross on the piece of paper, initiate the reaction process and use a timer or stopwatch to measure the length of time which passes before you can no longer see the cross. There are disadvantages to this method of observation as a lot of it is down to personal human judgement.

  1. Change in mass (usually gas given off)

All reactions that involve the production of gases can be conducted on a mass balance or scales. It is easy to measure the mass which escapes with this method of observation by recording the starting mass and the mass once the reaction has finished and subtracting the latter from the first. It is also easier to determine when the reaction has finished because the mass will cease to decrease.

  1. The volume of gas given off

The use of a gas syringe is usually necessary with this method of observation because it makes it easy to measure the volume of gas given off during a reaction. For example, immediately after initiating the reaction, you could time for a certain length of time, and record how much gas has been produced from the reaction at certain time intervals.

VARIABLES AND COLLISION THEORY:

There are four main factors or variables which influence the rate of a reaction, and they are:

  1. TEMPERATURE
  2. CONCENTRATION        (or pressure for gases)
  3. CATALYST
  4. SIZE OF PARTICLES        (or surface area)

THE COLLISION THEORY:

The collision theory perfectly explains rates of reaction and the involvement of each of the four factors above and their effects on rates of reaction. For a chemical reaction to take place, the particles of the reactants must collide with a sufficient amount of energy. The rate of reaction depends on how often the particles collide, and the amount of energy they collide with.

The more particle collisions there are in a reaction, the faster the rate of reaction. Therefore, to speed up a reaction you must somehow increase the number of times the particles of the reactants collide.

  1. TEMPERATURE

The temperature can affect the number of collisions between the particles of the reactants. The higher the temperature the more collisions there are, and the opposite is the case for a decrease in temperature. This is because an increase in temperature will cause the particles to move quicker as the heat gives them more energy to move around and therefore, there is a greater likelihood of collisions taking place. Also, particles are more likely to react when they are moving faster and collide, than when they simply collide and bounce off each other:

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Reactions only happen if the particles collide with sufficient energy. At a higher temperature there will be more particles colliding with sufficient energy to make the reaction happen at a much more rapid rate. This initial energy is known as activation energy and it is needed to break the initial bonds that exist between some of the reactant particles. In other words, the activation energy is the minimum amount of energy required for a reaction to take place.

  1. CONCENTRATION (or PRESSURE)

An increase in the concentration of the reactant particles will cause an increase ...

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