Unit 3 Energy and States

1. Unit 3 Energy and States

2. The State of Matter of a substance depends on several things • Attraction between particles called IMF or Inter-Molecular Forces • Solids have very high IMF • Gases have no attraction between molecules • Liquids have IMF a bit lower than solids • Energy of the particles • Space between particles

3. Phase Changes • Energy added • Melting: Solid to Liquid • Vaporizing: Liquid to Gas • Sublimation: Solid to Gas • Energy removed • Freezing: Liquid to Solid • Condensing: Gas to Liquid • Deposition: Gas to Solid

4. Heating curve Gas Temperature Vaporizing Liquid Melting Solid Time

5. Gas cooling curve Condensing Temperature Liquid Freezing Solid Time

6. Energy - capacity for doing work • weightless, odorless, tasteless • All chemical reactions and changes in state involve either: • release of energy, or • absorption of energy

7. The Law of Conservation of Energy states that in any chemical or physical process, energy is neither created nor destroyed. • All the energy is accounted for as Eth, Eph or Ech.

8. Endothermic Reactions • Eth flowing into a system from it’s surroundings: • Q has a positive value • system gains heat (gets warmer) as the surroundings cool down

9. Exothermic reactions • Heat flowing out of a system into it’s surroundings: • Q has a negative value • system loses heat (gets cooler) as the surroundings heat up

10. Units • A calorie is defined as the quantity of heat needed to raise the temperature of 1 g of pure water 1 oC. • 1 Calorie = 1 kilocalorie = 1000 cal. • The Joule, the SI unit of heat and energy • 4.184 J = 1 cal

11. Heat Capacity - the amount of heat needed to increase the temperature of an object exactly 1 oC Depends on both the object’s mass and its chemical composition Specific Heat Capacity (abbreviated “C”) - the amount of heat it takes to raise the temperature of 1 gram of the substance by 1 oC

12. The higher a material’s specific heat the LONGER it take to heat up and the LONGER it takes to cool down. ex. metals have low specific heat they heat up and cool down quickly.

13. How to solve heat capacity problems: Q = mc∆T Q = mHv Q = mc∆T Q = mHf Q = mc∆T

14. Meaning of formula symbols Q = heat or energy unit calories or kilocalories or joules or kilojoules (1 cal = 4.18 joules) m = mass in grams c = specific heat – the amount of energy or heat needed to raise 1 gram of something 1°C, it is different for each substance and phase of matter. J/g°C or cal/g°C ∆T = Change in temperature (Tempfinal – Tempinitial) Hf = Heat of fusion or melting. The amount of heat or energy needed to melt or freeze something. Energy needed for a phase change. Hv = Heat of vaporization or condensation. The amount of heat or energy needed to vaporize or condense something. Energy needed for a phase change.

15. Energy Constants For water c solid = 2.1 J/g°C or 0.5 cal/g°C 1 kcal = 1000 cal c liquid = 4.18 J/g°C or 1 cal/g°C 1 kJ = 1000 J c vapor = 1.8 J/g°C or 0.44 cal/g°C Hf = 334 J/g or 80 cal/g Hv = 2260J/g or 540 cal/g