Rates of Reaction.

Authors Avatar

Paul Dunn - 9242        Chemistry Coursework        Helsby High School -

                40411

Rates of Reaction Coursework

Introduction

A chemical reaction is the process in which substances change into other substances.  Chemical reactions can only take place when atoms, molecules, or ions collide with each other in order to share or exchange electrons.  What happens in chemical reactions is that bonds are broken down, and new ones are made instead.  To start a chemical reaction, reactants are needed in order to mix and chemically combine to give products.  The rate at which the products are formed is called the rate of reaction.  In this investigation, the reactants that will be used are magnesium and hydrochloric acid.  The products I will finish with will be magnesium chloride and hydrogen gas.  Following the reactivity series, magnesium is shown as a more reactive chemical than hydrogen.  In a displacement reaction, the more reactive metal will displace the less reactive metal from solutions of its compound.  And so, this explains why magnesium displaces hydrogen, producing magnesium chloride and creating hydrogen.  I know that different chemical reactions take place at different rates.  This is proven through usual daily life occurrences.  The ripening of fruit is an example of very slow chemical reactions.  Precipitation is an ideal example of a very fast chemical reaction.

Preparation

The object of the experiment is to discover what affects the rate of reaction when hydrochloric acid and magnesium are combined to form a solution.  To measure the reaction I plan to assess how much oxygen is created when the substances react.  The aim of the reaction is to discover how much hydrogen is produced, via different concentrations, in a certain amount of time.

The rate of a reaction is the speed at which reactants react to form a product. If there is a low rate of reaction it means that the molecules have less energy and therefore react at a slower speed. If there is a high rate of reaction it means that the molecules have a large amount of energy therefore react at a faster speed.

The chemical equation for the experiment I am to carry out is:

Magnesium        +        Hydrochloric acid                Magnesium Chloride        +Hydrogen

Mg                +        2HCl                                MgCl2                        +H2

The chemical reaction takes place when the magnesium ribbon is dropped into the hydrochloric acid.  The magnesium reacts with the hydrochloric acid because neither atom has a full outer shell of electrons.  When the two chemicals react a displacement reaction will take place and the magnesium will displace the hydrogen in the hydrochloric acid forming magnesium chloride and hydrogen gas.

For two substances to react, their particles must collide together.  Every time such a collision occurs there is the chance of a chemical reaction.  Anything that increases the number of collisions taking place will increase the rate of reaction.  A catalyst is a substance that increases the rate of a specific reaction without chemically changing in the process.  Catalysts lower reactions’ activation energy - the reaction needs less energy to start and develop.  The minimum energy required for a 'successful' collision is known as the activation energy (more energy can be focused on the task of producing successful collisions as oppose to the reaction itself).

Variables

There are a number of potential variables in this investigation:

  • Temperature                
  • Concentration of hydrochloric acid
  • Amount of Magnesium
  • Surface area of Magnesium
  • Catalysts

To perform this experiment I have to choose one of the above as a variable so I will be able to evaluate the results.  If I didn’t do this, the results would possess little or no correlation.

If I varied the temperature, this would be exceedingly difficult, as to get both the hydrochloric acid and the magnesium to a specific initial temperature would be problematical.  The temperature is also difficult to control, as it never remains constant.  This reaction is exothermic and so produces heat, so the temperature will change during the reaction.  When the temperature of a solution is raised, the molecules have more energy and spring back and forth move violently and frequently. When they move like this, they are more likely to collide.  This means they are also more likely to combine.  When the temperature is lowered, the molecules are slower and collide less.  That temperature-drop lowers the rate of the reaction.

To measure the surface area of the magnesium I would have to add to the hydrochloric acid would be almost impossible, as an area would have to be calculated, resulting in incredibly awkward decimal answers.

If a large molecule is crumbled into fine powder and placed in a solution, compared to the reaction time of a substance with more surface area (which has not been crumbled), it reacts faster, as all the little particles have a large surface area in contrast to the substance that has not been divided.

 

The amount of magnesium is a possible variable but in relation to the simplicity of the ‘concentration variable’, is still seems more difficult in comparison.

The more of a substance in a solution, the higher the chance of molecules colliding and speeding up the rate of the reaction.  If there is less of a substance there will be fewer collisions and the reaction will take place at a slower speed.

Join now!

To use one or more catalysts in my experiment may leave me with inaccurate results as catalysts are hard to control and there is not a known catalyst for this experiment anyway.  If you introduce a catalyst to a solution all you are doing is giving the reacting particles a place to stick to so they can collide into each other.

Considering these possible choices, I have decided to change the concentration of the hydrochloric acid, as this is one ...

This is a preview of the whole essay