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Heat with Phase Change Worksheet. 1) How many joules are required to heat 250 grams of liquid water from 00 to 1000 C ? 2) How many joules are required to melt 100 grams of water? 3) How many joules are required to boil 150 grams of water?
Explain changes in heat during changes of state, and describe latent heats of fusion and vaporization; Solve problems involving thermal energy changes when heating and cooling substances with phase changes
Explain the construction and use of a typical phase diagram. Use phase diagrams to identify stable phases at given temperatures and pressures, and to describe phase transitions resulting from changes in these properties. Describe the supercritical fluid phase of matter.
1. What is latent heat? 2. Why does the temperature of H2O not increase when it is boiling? Explain your answer by drawing a heating/cooling curve for water. 3. Describe the difference between latent heat of fusion versus latent heat of vaporization. Which process involves energy being absorbed? 4.
The heat Q required to change the phase of a sample of mass m is given by \(\mathrm{Q=mL_f}\) (melting or freezing) and \(\mathrm{Q=mL_v}\) (evaporating or condensing), where \(\mathrm{L_f}\) and \(\mathrm{L_v}\) are the latent heat of fusion and the latent heat of vaporization, respectively.
We examine the effects of phase change more precisely by considering adding heat into a sample of ice at \(-20^{\circ} \mathrm{C}\) (Figure \(\PageIndex{3}\)). The temperature of the ice rises linearly, absorbing heat at a constant rate of \(0.50 \ \mathrm{cal} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\) until it reaches \(0^{\circ} \mathrm{C}\).
Melting a solid requires an input of energy (at constant temperature) to loosen up the molecular or atomic bonds. Vaporizing a liquid involves an input of energy to increase the separation between molecules. Here, the latent heat involves a change in internal energy, plus work in expanding the volume.
