2.3 Thermal Energy Transfer In The Hydrosphere

The Unique Properties of Water High Surface Tension More than one state High Melting & Boiling Points Density High Specific Heat Capacity Unique heat of Fusion Unique heat of Vaporization

1. High Surface Tension Caused by adhesive and cohesive forces of attraction Enables insects and other organism to walk on the surface

2. More Than One State solid sublimation melting freezing liquid gas It can exist in 3 phases …..change occurs when energy is added or taken away solid sublimation melting freezing liquid gas

endothermic changes of state: -melting, evaporation, sublimation (solid to gas) exothermic changes of state: -freezing, condensation, sublimation (gas to solid)

When water has changed from one state to another a phase change has occurred Gas Graph showing phase changes Liquid Solid

3. High Melting and Boiling Points Allows for a wide range of temperatures on earth

4.Density Freezes it forms a solid crystal lattice Water is most dense at 4ºC (when it is still a liquid) At O ºC Water: Freezes it forms a solid crystal lattice molecules are farther apart making it less dense …. enabling it to float

Water freezes on the surface first (top to bottom) What would happen to organisms if ice formed at the bottom first? 20 ºC 4 ºC 0 ºC

5. High Specific Heat Capacity Water absorbs a lot of energy and releases it slowly…. helping to moderate coastal temperatures Specific Heat: Is the amount of energy to raise 1g of a substance 1ºC ….it is high for water

Quantity of Thermal Energy Is represented as Q It is the amount of thermal energy absorbed or released when temperature changes

to calculate heat energy use the following formula: Q = mcΔt where: Q = heat energy in Joules (J) m = mass in grams (g) Δt = change in temperature in °C c = specific heat capacity in J/gC

Example 1 Calculate the heat required to raise the temperature of 200 g of ethanol from 20.0°C to 45.0°C. Q = mcΔt = (200 g)(2.46 J/gC) (45.0C - 20.0 C) = 12 300 J = 1.23  104 J

Example 2 Calculate the heat required to raise the temperature of 400 g of ethanol from 10.0°C to 50.0°C. Q = mcΔt = (400 g)(2.46 J/gC) (50.0C - 10.0 C) = 39360 J = 3.94  104 J

6. Unique Heat of Fusion Hfus = Q n Q = nHfus Is the amount of energy required to convert 1 gram of solid into a liquid state Hfus = Q n Q = nHfus or where: Hfus = heat of fusion in J/mol or kJ/mol n = number of moles in mol Q = heat energy in J or kJ

Example 1 Calculate the heat of fusion of sulphuric acid if 2000 J of heat energy is applied to 0.694 mol. Hfus = Q/n = 2000 J/0.694 mol = 2881.8… J/mol = 2.88  103 J/mol

Example 2 Calculate the heat of fusion of sulphuric acid if 1050 J of heat energy is applied to 0.231 mol. Hfus = Q/n = 1050 J/0.231 mol = 4545.45… J/mol = 4.55  103 J/mol

7. Unique Heat of Vaporization Is the amount of energy that is needed to convert 1 gram of a liquid into gas Hvap = Q n or Q = nHvap where: Hvap = heat of vaporization in J/mol or kJ/mol n = number of moles in mol Q = heat energy in J or kJ

Example 1 Calculate the heat of vaporization of ethanol if 5000 J of heat energy is applied to 0.325 mol. Hvap = Q/n = 5000 J/0.325 mol = 15384.6…J/mol = 1.54  104 J/mol

Heating Curve For Water Temperature (C) Time (min) phase change H2O(l)  H2O(g) H2O(g) temperature change BP 100C Temperature (C) H2O(l) temperature change phase change H2O(s)  H2O(l) MP 0C H2O(s) temperature change Time (min)