Conservation of Mass/Energy and Specific Heat 12/4/2018
Potential & Kinetic Energy Chapter 2B: Energy, Matter, and Separating Mixtures Updated 10-18-04 Potential & Kinetic Energy Potential Energy (PE): stored energy Kinetic Energy (KE): Energy in Motion. KE = ½ mv2 m = mass v = velocity (speed) 12/4/2018 (c) 2004 Tim Bass
Law of Conservation of Energy Law of Conservation of Energy: Except for nuclear reactions, energy is neither created nor destroyed. The total amount of energy is constant in a system. The total amount of energy of a system is equal to the sum of potential energy and kinetic energy. PE + KE = Total Energy 12/4/2018
Total Energy Potential Energy (PE) Kinetic Energy (KE) KE + PE = Total Energy of System If KE goes up then PE must go down if the law of conservation of energy is true. If PE goes up then KE must go down if the law of conservation of energy is true. Pushing ball up a hill example. 12/4/2018
KE + PE = Total Energy of System Kinetic Energy Potential Energy Decreases Increases Increases Decreases 12/4/2018
Temperature Temperature: the concentration of heat. Kinetic Theory: Heat = the average kinetic energy of a substance. Measures the motion of molecules. Kinetic Theory: Temperature = average speed2 X mass 12/4/2018
Temperature & Kinetic Energy 12/4/2018
Heat Heat: Measures the total thermal (kinetic) energy of a system. Heat depends on the quantity of matter and the ability of the matter to store that energy (Specific Heat). 12/4/2018
Distinguish between Heat and Temperature Total amount of thermal (kinetic) energy. Total Energy Measured in Joules (J) Depends upon: Temperature of the matter. Mass of the matter. Specific Heat of the matter. Temperature Measures the intensity of heat. Average Kinetic Energy Measured in degrees Celsius (oC) 12/4/2018
Heat Calculations Change in heat = Mass x ΔT x Specific Heat q= m ΔT Cp m = mass ∆ = Change T = Temperature Cp = Specific Heat 12/4/2018
Temperature vs Heat The two different systems each had a change of 250 kJ of energy even though they had different amounts of water and different changes in temperatures. 12/4/2018
Gas Info: Other Kinetic Theory Information Particle motion: atoms move in a straight line between collisions. Pressure: the force of particles striking a surface. Temperature: a measure of the average kinetic energy of the particles of matter (speed). 12/4/2018
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Kinetic Energy In terms of the kinetic theory, for a molecule to change state it must gain enough energy to overcome inter-molecular attraction forces. A change of state can occur at any temperature. Sublimation: The change of solid to gas. Evaporation: The change of liquid to gas below boiling temperature. Condensation: The change of gas to liquid. 12/4/2018
Endothermic/Exothermic Changes Remember: Heat measures total amount of energy. Temperature measures heat intensity. Therefore Cold is the lack of thermal energy (heat). Law of Conservation of Energy: In a chemical reaction the total amount of energy is conserved. The energy of the reactants is equal to the energy of the products!
Chapter 2B: Energy, Matter, and Separating Mixtures Updated 10-18-04 Energy Changes Exothermic Change: Energy is released to the surroundings. Temperature goes up. - Δ H or energy shown as product A loss of heat energy Endothermic Change: Energy is absorbed from the surroundings. Temperature goes down. + Δ H or energy shown as reactant. A gain of heat energy Pg 43 #6-7 (8 is story link) Pg 45 9-11 Pg 66 #10-21 (c) 2004 Tim Bass
Energy Changes A + B AB + 50 kJ A + B AB; -50 kJ (Same Statement) Assume that A + B had a total of 100 kJ. Therefore, AB has a total energy level of 50 kJ (100 kJ – 50 kJ = 50 kJ). The additional 50 kJ will be given to environment The temperatures will typically go up. A + B AB; -50 kJ (Same Statement)
Energy Changes A + B + 50 kJ AB A + B AB; 50 kJ (Same Statement) Assume A + B contains a total of 100 kJ. Therefore AB contains 150 kJ (100 kJ + 50 kJ = 150 kJ) The 50 kJ will come from environment. Generally temperatures will go down. A + B AB; 50 kJ (Same Statement)