Question

a student carefully drops a 9.0 g solid zn pellet initially at 50.0 °c into an insulated cup containing 30.0 g of water at 27.8 °c. the student predicts that the temperature of the water will increase after the pellet is added. which of the following statements is the best justification for the student’s prediction?
a the metallic bonds between zn atoms will break when the zn is exposed to the water molecules, releasing energy that will be absorbed by the water molecules.
b collisions between the water molecules and the surface of the zn pellet will result in the transfer of energy, increasing the average kinetic energy of the water molecules.
c the strength of the hydrogen bonds between the water molecules will increase when the zn pellet is added, decreasing the average kinetic energy of the water molecules.
d collisions between zn atoms in the solid will increase in frequency when the zn is exposed to the water molecules, resulting in the transfer of energy to the surroundings.

Explanation:

• Option A: Metallic bonds in Zn don't break when added to water (Zn is solid, no reaction here to break bonds), so A is wrong.
• Option B: The Zn pellet is at a higher temperature (50.0°C) than water (27.8°C). When they come in contact, energy transfers from Zn (higher temp, more kinetic energy of atoms) to water molecules via collisions. This increases the average kinetic energy of water molecules, raising its temperature. This matches the prediction.
• Option C: Adding Zn doesn't increase hydrogen bond strength of water; also, increased bond strength would not increase water's temperature (kinetic energy would decrease, but that's not the case here), so C is wrong.
• Option D: Collisions between Zn atoms in solid don't increase in frequency due to water; also, energy transfer here is from Zn to water, but the reasoning about Zn atom collisions is incorrect, so D is wrong.

Answer:

B. Collisions between the water molecules and the surface of the Zn pellet will result in the transfer of energy, increasing the average kinetic energy of the water molecules.