States of Matter

Heat vs. Hot Heat is a form of energy and is measured in joules or calories Hotness is measured as temperature Temperature is directly proportional to kinetic energy

Temperature and Kinetic Energy Temperature is directly proportional to Kinetic Energy of the particles Kinetic Energy (energy of particle motion) = ½ mv2 where m is mass of particle and v is velocity of particle ALL PARTICLES ARE MOVING AT ALL TEMPERATURES ABOVE ABSOLUTE ZERO

Distribution of Energies Individual particles’ energies vary. Temperature depends on the average kinetic energy of all the particles.

Phase Changes Phase changes involve a change in Potential Energy, not Kinetic Energy THERE IS NO CHANGE IN TEMPERATURE UNTIL THE ENTIRE SAMPLE HAS COMPLETED PHASE CHANGE

Endothermic Phase Changes Heat must be absorbed by sample (Surroundings get cold as heat is transferred INTO system) Melting: solid to liquid Sublimation: solid to gas Vaporization: liquid to gas

Exothermic Phase Changes Material releases heat to the surroundings. (Surroundings get hot as heat is transferred from the system.) Condensation: gas to liquid Deposition: gas to solid Freezing: liquid to solid

Forces of Attraction Strongest to Weakest InTERmolecular 4. Hydrogen bonds Polar Compounds with H 5. Dipole-Dipole Polar with no H 6. (London) Dispersion Forces Nonpolar InTRAmolecular 1. Ionic 2. Metallic 3. Covalent The stronger the force, the more energy it takes to break it.

Heat and Phase Change Calculations Freezing and Melting The energy required to melt 1 mole of a substance is called the molar heat of fusion. The energy released by freezing 1 mole of a substance is the molar heat of fusion.

Heat and Phase Change Calculations Vaporizing and Condensing The energy required to convert 1 mole of a liquid substance to gas is the molar heat of vaporization. The energy released by when 1 mole of gas condenses to liquid is the molar heat of vaporization.

Example Problem 1 Calculate the energy required to melt 8.5 g of ice at 0° C. The molar heat of fusion for ice is 6.02 kj/mol. 8.5 g H2O x 1 mol H2O x 6.02 kj = 2.8 kj 1 18.0 g H2O mol H2O

Example Problem 2 Calculate the energy released when 25 g of steam at 100.°C condenses and cools to 55° C. The molar heat of vaporization is 40.6 kj/mol. Process 1: Condensation 25 g H2O x 1 mol x 40.6 kj = 57 kj released 1 18.0 g 1 mol Process 2: Cooling Q = mCΔt (25 g) ( 4.18 j/g°C) ( 55°-100.°C) = 4700 j released Total Energy Released = 57 kj + 4.7 kj = 62 kj