Liquids and Solids

Phase Changes Solid to Liquid Melting Fusing Ice melts at 0 degrees Celsius

Phase Changes Liquid to gas vaporization Evaporation Boiling A vapor is the gas phase of a substance that is liquid at room temperature water boils at 100 degrees Celsius

Phase Changes Gas to Liquid Condensation Water vapor condenses to water liquid at 100 degrees Celsius

Phase Changes Liquid to Solid solidification freezing Crystallization water freezes at 0 degrees Celsius

Solid to Gas (skip liquid) Phase Changes Solid to Gas (skip liquid) sublimation Dry ice (Solid carbon dioxide) sublimes into carbon dioxide gas at room temperature

Gas to Solid (skip liquid) Phase Changes Gas to Solid (skip liquid) deposition Water vapor deposits into ice crystals on cold surfaces

Heating Curve

Heating Curve of Water

Cooling Curve

Cooling Curve gas condensing liquid freezing solid

During a phase change: The temperature does not change (flat line) Average kinetic energy does not change Potential Energy changes!

KE increases PE increases

Energy equations Q = mcΔt Can only be used when there is no phase change occurring

Energy equations Q = mhf Can only be used when there is melting or freezing occurring Hf is the heat of fusion (Notice there is no temperature term, since temp does not change)

Hv is the heat of vaporization Energy equations Q = mhv Can only be used when there is boiling or condensing occurring Hv is the heat of vaporization (Notice there is no temperature term, since temp does not change)

Example # 1 Which equation would you use for this problem? How many joules of heat are absorbed when 50 g of water is heated from 30.2 degrees C to 58.6 degrees C? Q = mcΔt

Answer Q = 50g x 4.18 J/goc x (58.6 – 30.2 oC) Q = 5936J

Example # 2 Which equation would you use for this problem? How many joules of heat are required to melt 225 g of ice at 0 degrees C? Q = mHf

Answer Q = 225g x 334 J/g Q = 75,150 J Q = 75.15 kJ

Example # 3 Which equation would you use for this problem? How many joules of heat are required to vaporize 423 g of water at 100 degrees C? Q = mHv

Answer Q = 423g x 2260 J/g Q = 955,980 J Q = 955.98 kJ

Why does boiling 1 g of water require so much more energy than melting 1 g of water? Boiling = 2260 J/g Melting = 334 J/g

Lots of energy needed to separate the particles from liquid to gas