To plan an investigation that allows me to measure the effect of increasing the concentration of a reactant on the rate of reaction. With the results generated, it is also hoped to draw accurate conclusions and explain the results using scientific knowledge. Introduction
Some reactions are fast, for example neutralisation or burning magnesium in air to produce magnesium oxide. However, other reactions can be slow, for example, rusting of iron or souring of milk. The speed at which a reaction takes place is called its rate of reaction.
Reactions can happen at different speeds, but the speed of a chemical reaction can be altered by changing certain controlling factors, these factors include: 1. Temperature
2. Surface Area
To understand how these controlling factors can alter the rate of a chemical reaction, it is firstly important to understand how a chemical reaction takes place. To understand how reactions take place, we use the collision theory. Collision Theory
The collision theory states that for a reaction to take place between reacting particles (ions, molecules or atoms), it is essential that they collide. B
The collision theory goes further to state that for a reaction to take place, there must be sufficient energy in the collision. If there isn’t sufficient energy, the colliding particles simply bounce off each other.
Compound A-B formed when the collision has sufficient energy. Atom B
When two particles collide with sufficient energy and the product is formed, the collision is said to be an effective collision. The minimum energy in a collision that is needed to bring about a chemical reaction (effective collision) is known as the Activation Energy.
Controlling Factors for Rates of Reactions
In a chemical reaction when the temperature increases the reacting particles gain kinetic energy and therefor move faster. As the particles are moving faster, there are more collisions. As there are more collisions, the rate of reaction is increased. Also, as the particles are moving faster, there is greater energy, more of them will be effective collisions, and therefor the rate of reactions is increased because more of the particles now have the activation energy to bring about a chemical reaction.
From the graph, it is seen that as the temperature is increased, the time for the reaction is reduced, and the rate of reaction is increased.
An investigation was used to prove that the increasing temperature of a reactant can increase the rate of a chemical reaction. 50cm³ of 1 molar hydrochloric acid was placed into a beaker. To this was added 2.0g of marble chip. The time taken for the effervescence to stop was then recorded. Another 50cm³ of 1 molar hydrochloric acid was measured into a beaker. This was warmed until it reached 50°c. To this was also added 2.0g of marble chips, and the time for the effervescence to stop was recorded. Table of Results
Temperature of 1 Molar HCl (aq) in °c| Time taken for Effervescence to Stop| 20°c| 15m 45s|
50°c| 13m 36s|
As the temperature of the acid was increased, the time taken for the effervescence to stop decreased. As the acid is heated, the particles gain more energy and move about faster. This leads to more collisions, which will be effective, due to the particles increased energy. Therefor increasing the temperature of a reactant increases the rate of reaction.
2. Surface Area
Reactions only happen at the surface of a reactant, since it is the particles at the surface that have a chance to collide. By surface area, we mean the amount of surface that is available to take part in a reaction.
Small Surface Area
Only 12 particles at the surface available for collision
Larger Surface Area
16 particles at...