.The amount of energy involved in melting a substance without changing its temperature is called the A) heat of vaporization. B) calorie. C) joule. D) heat of fusion. E) heat of combustion.

Define the joule in terms of SI base units.

Are changes in state physical or chemical changes? Explain. What type of forces must be overcome to melt or vaporize a substance (are these forces intramolecular or intermolecular)? Define the molar heat of fusion and molar heat of vaporization. Why is the molar heat of vaporization of water so much larger than its molar heat of fusion? Why does the boiling point of a liquid vary with altitude?

9.21 Which type of energy heat or work, is valued more by society? What evidence supports your judgment?