College of Massage Therapists of British Columbia (CMTBC) Practice Exam

How many calories does it take to convert 1 gram of solid ice to a liquid?

1. 50 calories

2. 80 calories

3. 100 calories

4. 20 calories

The correct answer is: 80 calories

The correct answer is associated with the concept of latent heat, specifically the latent heat of fusion. To convert 1 gram of solid ice at 0 degrees Celsius to liquid water at the same temperature, it requires 80 calories of heat energy. This energy does not raise the temperature of the ice or water but instead changes the state from solid to liquid. The reason 80 calories is necessary is due to the molecular structure of water. When ice is heated, the energy first goes into breaking the hydrogen bonds that hold the water molecules in a solid structure, rather than increasing the overall temperature of the substance. This process explains why, despite applying heat, the temperature remains constant until all ice has melted. Other values typically associated with the conversion of ice to water are not accurate for this specific phase change. Thus, the requirement of 80 calories to achieve the phase change from solid ice to liquid water is essential to understand in the context of thermodynamics and energy transfer in physical chemistry.