Essay About Rate Of Reaction And Black Cross

Investigating Rates Of Reaction
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Rate of Reaction – Sodium Thiosulphate and Hydrochloric Acid
Investigation, to find out how the rate of reaction between Sodium
Thiosulphate and Hydrochloric acid is affected by changing the
concentration.
Introduction
I must produce a piece of coursework investigating the rate of
reaction, and the effect different changes have on them. The rate of
reaction is the rate of loss of a reactant or the rate of development
of a product during a chemical reaction. It is measured by dividing 1
by the time taken for the reaction to take place. There is five
factors which affect the rate of a reaction, according to the
collision theory of reacting particles: temperature, concentration (of
solution), pressure (in gases), surface area (of solid reactants), and
catalysts. I have chosen to investigate the effect of concentration on
the rate reaction. This is because it is the most practical to
investigate. Dealing with temperatures is a difficult task especially
when we have to keep constant high temperatures. Secondly the rate
equation and the constant k changes when the temperature of the
reaction changes. We have no gases and solids involved therefore it is
easy to deal with solutions. Similarly the use of a catalyst
complicates things, and if used incorrectly could alter the outcome of
the experiment.
The theory behind this experiment is that Increasing the
concentration can increase the rate of the reaction by increasing the
rate of molecular collisions.
GRAPH
I will place the reaction mixture on a paper with a black cross-drawn
on it. When the cross is completely obscured, the reaction will have
finished. The time taken for this to happen is the measure of the rate
of reaction. We must do this several times, and change the
concentration of Sodium Thiosulphate.
The rate of reaction is a measure of the change, which happens during
a reaction in a single unit of time. The things that affect the rate
of reaction are as follows:
* Surface area of the reactants
* Concentration of the reactants
* The temperature at which the reaction is carried out
* Use of a catalyst
Reaction equation is mentioned above but rate equation could only be
decided by doing experiments. So the following procedure can be used
to carry out the experiment.
Plan
Equipment
* 2 Measuring cylinders
* Beaker
* Stopwatch
* Paper with black cross on it
* Sodium Thiosulphate (different concentrations)
* Hydrochloric acid (same concentration each time)
* Water (different concentrations)
* Pipette
Prediction
I predict that the greater the concentration of Sodium Thiosulphate
solution the faster the chemical reaction will take place. Therefore,
the cross will disappear more quickly due to the cloudiness of the
solution. I predict that as concentration is doubled the amount of
time taken for the reaction is halved. This means that both graphs
drawn up in my analysis will have positive correlation, and will
probably be curved as the increase in rate of reaction will not be
exactly the same as the concentration is increased. This can be
justified by relating to the collision theory.
If solutions of reacting particles are made more concentrated there
are more particles per unit volume. Collisions between reacting
particles are therefore more likely to occur. All this can be
understood better with full understanding of the collision theory
itself: For a reaction to occur particles have to collide with each
other. Only a small percent result in a reaction. This is due to the
energy barrier to overcome. Only particles with enough energy to
overcome the barrier will react after colliding. The minimum energy
that a particle must have to overcome the barrier is called the
activation energy, or Ea. The size of this activation energy is
different for different reactions.
I think that the concentration of a solution effects the rate of
reaction because the rate of reaction depends on how frequently the
molecules of the reacting substances collide. A more concentrated
substance