Question

I recently did an experiment where we had to discover the rate order of the sufrace area of magnesium and hydrochloric acid as well as the activation energy. The point of the experiment was to discover the kinetic parameters of a heterogenous reaction. As I was writing my lab report, I uncovered a similiar experiment however the rate order for their experiment for hydrochloic acid was 2 when mine came out as 1. So I was curious as to how is it possible for the same experiment to produce different rate orders? What factors could change the rate order of a reactant? Thank you for any help you can give me.

Answer 1

The reaction between Magnesium and Hydrochloric acid equation given by :

Mg_(s) + 2HCl_(aq) MgCl_2(aq) + H_{2 (g)}

If the experimental procedures followed were standard for all 2 sets of experiment including the mode of collecting data, then the results obtained would be same.

Suspected error :

1) If for a solid magnesium used, there was slight difference in weight.

2) Determining the end of reaction would be uncertain. Even after disappearance of magnesium, gas bubbles were evident , implying reaction was incomplete. That would lead to error in stopwatch reading and error in determining order of reaction.

Improvements in reaction :

1) Use at least 2 sets of experimental data to get average of result to minimize the impact of experimental error.

2) Choose only one indicator that signifies end of reaction

3) Suitably acid-base indicators can be used to detect the end of reaction accurately.

However, the reaction follows the first-order reaction.

Factors affecting the reaction rate :

1) Surface area of the solid reactant : Rate of heterogenous reaction depends on surface area of more condensed phase.

2) Concentration or pressure of reactant : As the concentration of reactant increases the reaction rate also increases.

3) Temperature of reactant : Increasing the temperature of system increases the kinetic energy of its particles and particles move faster and they collide more frequently . It increases the rate of reaction.

4) Nature of reactant

5) Presence or absence of catalyst : Most catalyst used are highly selective often determine the product of reaction by accelerating the reaction rate.