Rates of Reactions

Rates of Reactions

Aim:

I am going to investigate how the rate of the reaction between sodium

thiosulphate and hydrochloric acid depends on the concentration of

sodium thiosulphate.

The reaction rate of a chemical reaction is the speed of production of

products from reactants.

Sodium thiosulphate + hydrochloric acid ==> sodium chloride + sulphur

dioxide + water + sulphur

Na2S2O3 (aq) + 2HCl (aq) ==> 2NaCl (aq) + SO2 (aq) + H2O (l) + S(s)

The solid sulphur (S(s)) formed in this reaction makes the colourless

solution go cloudy.

Factors:

The factors I believe that will affect what happens in the

investigation are:

* Catalyst- A catalyst s a substance which alters the rate of a

chemical reaction but is chemically unchanged at the end of the

reaction.

- A catalyst speeds up a reaction; an inhibitor (a substance) slows it

down.

* Concentration- The more concentrated the faster the rate (note in

some cases the rate may be unaffected by the concentration of a

particular reactant provided it is present at a minimum

concentration). Remember for gasses, increasing the pressure

simply increases the concentration so that's the same thing.

* Surface area- greater surface area and since the reaction occurs

at the surface we get a faster rate.

* Temperature- Usually reactions speed up with increasing

temperature ("100C rise doubles rate").

The collision theory:

Particles need to collide with each other to react and the collision

theory is all about this. The can be affected by the temperature of

the particles, the concentration of the particles, whether a catalyst

is used or the surface area (if the particles are solid).

Temperature affects the rate of a reaction because if particles are

cold, they move slowly and there are few collisions between them. But

when they are heated up they move much faster or you can also say they

have more kinetic energy. When the move faster there is more of a

chance of a collision. More collisions means that the reaction goes

faster - its rate increases.

Concentration of the acid used also affects the rate because when

there is a higher concentration (more acid) there are more particles

to collide with each other-more collisions means that the reaction

goes faster.

A catalyst is a substance that can speed up a chemical reaction

without actually being used up in the reaction. It gives the particles

a surface to stick to so they can collide with each other there - more

collisions. Again when there are more collisions this causes the

reaction to go faster.

Surface area also affects the rate of a reaction if the particles are