Rates of Reaction: Question 1

Worked solution

Step 1: Identify what kind of reaction this is

Both silver nitrate and sodium chloride are already dissolved in water before they are mixed. The reaction that produces the white precipitate happens entirely in solution, between dissolved ions. No solid reactant is present at the moment the two liquids meet.

Step 2: Check each option against the factors that affect rate

• Option A (more concentrated silver nitrate solution): increasing the concentration of solutions increases the rate, because there are more particles per unit volume, so collisions between the two types of ion happen more often. This option would increase the rate.
• Option B (raising the temperature): increasing temperature always increases the rate of a reaction, including reactions that take place entirely in solution. This option would increase the rate.
• Option C (grinding the solid silver nitrate before dissolving it): the surface area of solids factor only applies while a reactant is still a solid, reacting at its surface. Once the silver nitrate crystals are fully dissolved, they no longer exist as a solid. The silver ions are already spread uniformly through the solution. Grinding the crystals beforehand has no effect on how fast the dissolved ions go on to collide and react. This option would not increase the rate.
• Option D (adding a catalyst): a catalyst increases the rate of a reaction by providing a pathway with a lower activation energy. This option would increase the rate.

Step 3: Select the answer

Only grinding the solid before it is dissolved has no effect on the rate of the reaction between the two solutions, because the surface-area factor stops applying once nothing solid remains.

Final answers

• $\boxed{\text{option C}}$. Grinding the silver nitrate crystals before dissolving them does not increase the rate, since surface area only affects reactions that involve a solid reactant.