Rates of reaction

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An excellent project, very perceptive -

BACKGROUND INFORMATION

What affects the rate of reaction?

1) The surface area of the magnesium.

2) The temperature of the reaction.

3) Concentration of the hydrochloric acid.

4) Presence of a catalyst.

In the experiment we use hydrochloric acid which reacts with the

magnesium to form magnesium chloride. The hydrogen ions give

hydrochloric acid its acidic properties, so that all solutions of

hydrogen chloride and water have a sour taste; corrode active metals,

forming metal chlorides and hydrogen; turn litmus red; neutralise

alkalis; and react with salts of weak acids, forming chlorides and the

weak acids.

Magnesium, symbol Mg, silvery white metallic element that is

relatively unreactive. In group 2 (or IIa) of the periodic table,

magnesium is one of the alkaline earth metals. The atomic number of

magnesium is 12.

Magnesium(s) + Hydrochloric acid(aq) = Magnesium Chloride(aq) +

Hydrogen(g)

Mg + 2HCl = MgCl2

+ H2

In the reaction when the magnesium hits the acid when dropped in,

it fisses and then disappears giving of hydrogen as it fisses and it

leaves behind a solution of hydrogen chloride.

The activation energy of a particle is increased with heat. The

particles which have to have the activation energy are those particles

which are moving, in the case of magnesium and hydrochloric acid, it is

the hydrochloric acid particles which have to have the activation energy

because they are the ones that are moving and bombarding the magnesium

particles to produce magnesium chloride.

The rate at which all reactions happen are different. An example

of a fast reaction is an explosion, and an example of a slow reaction is

rusting.

In any reaction,

reactants chemical reactions® products.

We can measure reactions in two ways:

1) Continuous:- Start the experiment and watch it happen; you can use a

computer "logging" system to monitor it. I.e. Watching a colour fade or

increase.

2) Discontinuous:- Do the experiments and take readings/ samples from

the experiment at different times, then analyse the readings/samples to

see how many reactants and products are used up/ produced.

Reaction rate = amount of reactant used up

time taken

If the amount used up is the same each time then the only thing

that changes is the time taken.

so, reaction rate µ 1

time taken.

rate = K

time taken.

Where K is the constant for the reaction.

For particles to react:-

a) They have to collide with each other.

b) They need a certain amount of energy to break down the bonds of the

particles and form new ones. This energy is called the "Activation

Energy" or Ea.

When we increase the temperature we give the particles more

energy which:

1) Makes them move faster which In turn makes them collide with each

other more often.

2) Increases the average amount of energy particles have so more

particles have the "activation energy"

Both of these changes make the rate of reaction go up so we see a

decrease in the amount of time taken for the reaction and an increase in

1

time taken.

= 1

time taken. Reflects the rate of reaction.

Because temperature has an effect on both the speeds at which the

particles react and the activation energy they have a greater effect on

the rate of reaction than other changes.

A change in concentration is a change in the number of particles

in a given volume.

If we increase the volume:-

a) The particles are more crowded so they collide more often.

b) Although the average amount of energy possessed by a particle does

not change, there are more particles with each amount of energy;- more

particles with the activation energy.

a) is a major effect which effects the rate, but b) is a minor

effect which effects the rate very slightly.

In this experiment we are not concerned with...
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