Factors that affect the rate of a reaction.

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Factors that affect the rate of a reaction

INTRODUCTION

The rate of a reaction is how long it takes for the products in a reaction to form or how rapidly the reactants get used up.

It is possible to tell something is reacting because odours and gases are given off, there can be a change in colour, change in ph level, fizzing and bubbling. A reaction will happen fastest at nearer the start of the reaction because this is when there is the most amounts of reactants, as the reactants get used up the rate of reaction is slower.

The rate of reaction is found by measuring the amount of a reactant used up per unit of time or the amount of a product produced per unit of time.

A reaction can be made to go faster or slower by changing  a number of factors. In order for a reaction to occur it is required that: particles must collide with each other and the collision must have enough energy. If this happens the original bonds are broken and new bonds are formed so that new products are formed.

The collision theory is related to the rate of a reaction. When collisions occur, they do not always result in a reaction.  If two colliding molecules have sufficient energy they will react. This is called the ‘activation energy’.  Successful collisions can be increased by a number of factors. These factors include:

  • Temperature – By heating the mixture the energy levels of the molecules involved in the reaction are increased. Increasing the temperature means the molecules move faster because more energy is being transferred to them (kinetic theory) and more collisions will take place.

  • Concentration – Increasing the concentration of the reactants will increase the frequency of collisions between two reactants. This is also collision theory. Although you keep the temperature constant, kinetic theory is relevant. This is because the molecules in the reaction mixture have a range of energy levels. The more concentrated a solution is the faster a reaction will happen.

  • Surface area – if one of the reactants is solid, the surface are of the solid will affect how fast the reaction goes. This is because the two types of molecule can only bump into each other at the solid’s surface. So the larger the surface area of the solid, the faster the reaction will be. For example, 10g of small chips has more surface area than 10g of large sized chips.

  • Amount – it is important to keep the amount of reactants constant in the experiment because, as the reactant(s) is used up, the reaction slows down. This means a smaller amount of solution will have a different reaction time to a large amount of solution. A small amount of solution will have fewer atoms in it so it will be less likely to collide as successfully compared to a more abundant amount of solution.

  • Catalysts – a catalyst increases the rate of a chemical reaction without itself being used up in the reaction. Catalysts are usually transition metals. In the presence of a catalyst, less activation energy is needed by a collision in order to be successful, it provides an alternative route. Therefore there are relatively more successful collisions and so the rate of reaction will increase.
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AIM

I am going to investigate how the concentration of the solution will effect the rate of reaction when calcium carbonate reacts with hydrochloric acid. The equation for this reaction is:

Calcium carbonate + hydrochloric acid  calcium chloride + water  + carbon dioxide

CaCO  (s)               + 2Cl (aq)                 CAcl  (aq)            + H 0(aq) + CO  (g)

To measure the rate of reaction I will measure how much gas is being given off rather ...

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