Which of the following will Increase the rate of reaction of Chips of a metal M as shown in the equation below? M(s)+2HC1(aq) → MCI2 (aq) + H2(g)

Analyze the question The reaction is M(s) + 2HCl(aq) → MCl₂(aq) + H₂(g). We are asked which change will increase the rate of reaction for chips of the metal.

Concept: factors affecting reaction rate (collision theory) A reaction happens when particles collide with enough energy. The rate increases when:

1. Concentration of reactants increases (more particles per unit volume)
2. Temperature increases (particles move faster and have more energy)
3. Surface area of a solid increases (more particles exposed to collide)
4. A catalyst is added
5. Pressure increases, but only for reactions involving gases as reactants

Evaluating each option

• A. Adding distilled water: This dilutes the acid, lowers its concentration, and slows the reaction. ✗
• B. Decreasing the temperature: Particles have less energy, so the rate drops. ✗
• C. Diluting the hydrochloric acid: The concentration falls, so there are fewer collisions and the rate drops. ✗
• D. Grinding the metal into powder: This greatly increases the surface area exposed to the acid, so there are more collisions per second and the rate rises. ✓
• E. Increasing the pressure: The reactants are a solid and an aqueous solution. Pressure has almost no effect on them. H₂ is only a product. ✗

Answer: The correct option is D. Grinding the metal into powder.

Exam tip: For solid reactants, remember "smaller pieces = bigger surface area = faster reaction". Pressure only matters when gases are reactants. Words like "dilute", "add water" and "lower temperature" almost always mean a slower rate.