How do concentration of a reactant and temperature affect the rate of a chemical reaction

In this experiment investigated rate of reaction between magnesium and hydrochloric acid

Mg + 2HCl —— MgCl2 + H2

What are you measuring

volume of hydrogen produced at different time intervals

Explain the procedure

• Add magnesium ribbon to a known volume of hydrochloric acid in a conical flask.

• Collect hydrogen gas using a gas syringe or inverted measuring cylinder over a trough ¾ full of water.

• Vary concentration of HCl (e.g. 0.5 M, 1.0 M) to see effect on rate.

• Vary temperature of acid using a water bath.

• Keep other variables (e.g. Mg length, acid volume) constant.

• Measure volume of gas at regular intervals to calculate rate.

• Trough is ¾ full to submerge collection tube without overflowing.

How does the rate of reaction change as the experiment proceeds and why does this happen

• Rate of reaction decreases over time.

• Hydrochloric acid concentration decreases as it is used up.

• Fewer H⁺ ions available to collide with magnesium.

• According to collision theory, fewer successful collisions occur per second.

• Reaction slows down, so hydrogen gas is produced more slowly.

• This is shown by the flattening of the gas volume vs time graph.5

What is the effect of increasing the concentration of the acid on the initial rate of reaction

• Increasing the concentration of hydrochloric acid increases the initial rate of reaction.

• Higher concentration means more acid particles per unit volume.

• This leads to more frequent collisions between H⁺ ions and magnesium atoms.

• More collisions increase the number of successful collisions per second.

• Therefore, the reaction starts faster, producing hydrogen gas at a quicker rate initially.