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?

Adding more solid X causes the solution’s temperature to rise further, indicating that more heat was released by the reaction. More solid reactant provides more particles that can collide with particles in solution Y, increasing the number of molecular collisions and allowing more reaction to occur. Therefore, the best choice is “It increased the number of molecular collisions.”

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