Chapter 10 Properties of Solids and Liquids 10.5 Changes of State Learning Goal Describe the changes of state between solids, liquids, and gases; calculate the energy involved.

Change of State Matter undergoes a change of state when it is converted from one state to another at a constant temperature. Figure 10.3 Changes of state include melting and freezing, boiling and condensation, sublimation and deposition.

Melting and Freezing A substance changes from a solid to a liquid at its melting point (mp) changes from a liquid to a solid at its freezing point (fp) Water has a freezing (melting) point of 0 °C.

Heat of Fusion The heat of fusion is the energy that must be added to convert exactly 1 g of solid to a liquid at its melting point. For H2O, 334 J of heat is needed to melt 1 g of ice at its melting point (0 °C). H2O(s) + 334 J/g  H2O(l) Endothermic

Heat of Fusion, H2O The heat of fusion is also the quantity of heat that must be removed to freeze 1 g of water at its freezing point (0 °C). For H2O, 334 J of heat is removed to freeze 1 g of ice at its melting point (0 °C). H2O(l)  H2O(s) + 334 J/g Exothermic

Heat of Fusion, H2O The heat of fusion for water can be used as a conversion factor. 1 g H2O = 334 J Calculating heat to melt (or freeze) water, we use the following equation:

Guide to Calculations, Heat of Fusion

Learning Check How much heat in joules is needed to melt 15.0 g of ice (H2O)?

Solution How much heat in joules is needed to melt 15.0 g of ice (H2O)? Step 1 State the given and needed quantities. Given: 15.0 g of H2O(s) at 0 °C Need: joules to melt ice at 0 °C

Solution How much heat in joules is needed to melt 15.0 g of ice (H2O)? Step 2 Write a plan to convert the given quantity to the needed quantity.

Solution How much heat in joules is needed to melt 15.0 g of ice (H2O)? Step 3 Write the heat of fusion factor and any metric factor needed.

Solution How much heat in joules is needed to melt 15.0 g of ice (H2O)? Step 4 Set up the problem and calculate the needed quantity.

Evaporation, Boiling, and Condensation Evaporation occurs when water molecules gain sufficient energy to escape the liquid surface and enter the gas phase.

Evaporation, Boiling, and Condensation At the boiling point, the molecules have enough energy to overcome their attractive forces and become a gas.

Evaporation, Boiling, and Condensation In condensation water vapor is converted to a liquid as the water molecules lose kinetic energy and slow down. Condensation occurs at the same temperature as boiling, but heat is removed.

Heat of Fusion, Vaporization for Selected Substances

Heat of Vaporization versus Heat of Fusion

Heat of Vaporization, H2O The heat of vaporization for water can be used as a conversion factor. 1 g H2O = 2260 J To calculate the heat needed to boil (or vaporize) water, we use the following equation:

Guide to Calculations, Heat of Vaporization

Learning Check How many kilojoules (kJ) are released when 50.0 g of steam from a volcano condenses at 100 °C ?

Solution How many kilojoules (kJ) are released when 50.0 g of steam from a volcano condenses at 100 °C ? Step 1 State the given and needed quantities. Given: 50.0 g of H2O(g) Need: kilojoules released to condense H2O(g) to H2O(l)

Solution How many kilojoules (kJ) are released when 50.0 g of steam from a volcano condenses at 100 °C ? Step 2 Write a plan to convert the given quantity to the needed quantity.

Solution How many kilojoules (kJ) are released when 50.0 g of steam from a volcano condenses at 100 °C ? Step 3 Write the heat of vaporization factor and any metric factor needed.

Solution How many kilojoules (kJ) are released when 50.0 g of steam from a volcano condenses at 100 °C ? Step 4 Set up the problem and calculate the needed quantity.

Heating and Cooling Curves All the changes of state during the heating of a solid can be illustrated using a heating curve. Heating curves are a graph, with temperature on the vertical axis and addition of heat on the horizontal axis. Heating curves illustrate a change of state, using a horizontal line in temperature of a substance as energy is added or released by a sloped line

Heating Curve, H2O Figure 10. 6 A heating curve diagrams the temperature increases and changes of state as heat is added.

Cooling Curve, H2O The cooling curve is a diagram of the cooling process and the reverse of a heating curve. A cooling curve for water illustrates the change in temperature and changes of state as heat is removed.

Combining Energy Calculations

Learning Check A plateau (horizontal line) on a heating curve represents A. a temperature change B. a constant temperature C. a change of state A sloped line on a heating curve represents

Solution A plateau (horizontal line) on a heating curve represents C. a change of state A sloped line on a heating curve represents A. a temperature change

Learning Check Use the cooling curve for H2O to answer each. A. Water condenses at a temperature of (1) 0 °C (2) 50 °C (3) 100 °C B. At a temperature of 0 °C, liquid water (1) freezes (2) melts (3) changes to a gas C. When water freezes, heat is (1) removed (2) added

Solution Use the cooling curve for H2O to answer each. A. Water condenses at a temperature of (3) 100 °C B. At a temperature of 0 °C, liquid water (1) freezes C. When water freezes, heat is (1) removed

Learning Check To reduce a fever, an infant is packed in 250. g of ice H2O(s). If the ice (at 0 °C) melts and warms to body temperature (37.0 °C), how many joules are removed?

Solution If 250. g ice (at 0 °C) melts and warms to 37.0 °C, how many joules are removed? Step 1 State the given and needed quantities. Given: 250. g H2O(s) H2O(l) water at 37.0 °C Need: joules to melt H2O(s) at 0 °C and warm to 37.0 °C

Solution If 250. g ice (at 0 °C) melts and warms to 37.0 °C, how many joules are removed? Step 2 Write a plan to convert the given to the needed quantity.

Solution If 250. g ice (at 0 °C) melts and warms to 37.0 °C, how many joules are removed? Step 2 Write a plan to convert the given to the needed quantity.

Solution If 250. g ice (at 0 °C) melts and warms to 37.0 °C, how many joules are removed? Step 3 Write the conversion factors needed.

Solution If 250. g ice (at 0 °C) melts and warms to 37.0 °C, how many joules are removed? Step 4 Set up the problem and calculate the needed quantity.

Solution If 250. g ice (at 0 °C) melts and warms to 37.0 °C, how many joules are removed? Step 4 Set up the problem and calculate the needed quantity.

Concept Check