Question

a reaction occurs when solid x is placed into solution y. as a result, the temperature of the new solution increases by 3°c. the temperature rises another 2°c when more of solid x is added to the solution. what does this indicate about the effect of adding more solid?
○ it increased the number of molecular collisions.
○ it decreased the number of molecular collisions.
○ it decreased the space between the molecules and lowered the reaction rate.
○ it increased the space between the molecules and increased the reaction rate.

Explanation:

When more solid X is added, the temperature of the solution rises further (another 2°C), indicating the reaction is releasing more heat (exothermic or reaction rate increasing). Adding more reactant (solid X) increases the number of reactant particles, leading to more frequent molecular collisions, which increases the reaction rate (and more heat release, causing temperature rise). Option B is wrong as adding reactant should increase collisions. Option C: decreasing space (e.g., concentration increase) would increase, not lower, reaction rate. Option D: adding solid (a reactant) doesn't increase space between molecules; it increases reactant amount for more collisions. So only A is correct.

Answer:

A. It increased the number of molecular collisions.