Chapters KD-7 Thermodynamics

Thermal Energy Thermal energy-The internal kinetic and potential energy of molecules

Heat vs Temperature Heat-Thermal energy that flows from 1 substance to another –Only flows from high to lower temps. –Symbol: Q –Measured in Joules or calories Heat-Thermal energy that flows from 1 substance to another –Only flows from high to lower temps. –Symbol: Q –Measured in Joules or calories

Heat Objects exchange heat until they reach equilibrium (same temp.)

Heat vs Temperature Temperature-A quantity proportional to the average kinetic energy of molecules –NOT energy –Symbol: T –Measured in °C, °F, or K Temperature-A quantity proportional to the average kinetic energy of molecules –NOT energy –Symbol: T –Measured in °C, °F, or K

Temp. and K.E. –Temp. increases, the K.E. of molecules increase, molecules move faster and expand

Important Temps. Temperatures for waterK°C°F Freezing/Melting point-Temp. where a liquid changes to solid or vice versa 273 KO °C32 °F Boiling (vaporization)/condensation point-Temp. Where a liquid changes to a gas (vapor) or vice versa 373 K100 °C212 °F Absolute zero-Temp. where molecular motion is at a minimum O K-273 °C-460 °F * There is 100° difference between boiling and freezing on BOTH Celsius and Kelvin, so when we deal with changes of temp. doesn’t matter if we use °C or K

To Convert: K = °C F = (9/5 °C) + 32 °C = 5/9 (°F-32) * To convert between Fahrenheit and Kelvin, you must 1 st convert to Celsius

Example: If the temperature is 75 °F outside, what is the temp. in Kelvin? °C = 5/9 (°F-32)°C = 5/9 (75°-32)°C = 24˚ K = °C + 273K = 24° + 273K = 297

Specific Heat Specific Heat-The thermal energy needed to change the temp. of 1 kg of a substance by 1 K (or 1 °C) –Heat added to raise a temp. or taken away to lower a temp. –Symbol: c –Measures in J/kg K Specific Heat-The thermal energy needed to change the temp. of 1 kg of a substance by 1 K (or 1 °C) –Heat added to raise a temp. or taken away to lower a temp. –Symbol: c –Measures in J/kg K

Specific Heat of Common Substances Pg. 46 in workbook

Heating/Cooling Curve

Change Temperature Amount of heat needed to change temp. use: Q = m c ∆T –Q = heat (J) –m = mass (kg) –c = specific heat (J/kg K) –∆T = change in temp. (K or C) Amount of heat needed to change temp. use: Q = m c ∆T –Q = heat (J) –m = mass (kg) –c = specific heat (J/kg K) –∆T = change in temp. (K or C)

Change State Amount of heat needed to change state use (materials DO NOT change temperature when they change states): Q = m Hf or Q = m Hv m = mass (kg) Hf = heat of fusion (J/kg) Hv = heat of vaporization (J/kg) Amount of heat needed to change state use (materials DO NOT change temperature when they change states): Q = m Hf or Q = m Hv m = mass (kg) Hf = heat of fusion (J/kg) Hv = heat of vaporization (J/kg)

Change State

Fusion vs Vaporization Heat of fusion- Amount of thermal energy needed to change 1 kg of a substance from a solid to a liquid or vice versa –For water: 3.34 X 10 5 J/kg Heat of fusion- Amount of thermal energy needed to change 1 kg of a substance from a solid to a liquid or vice versa –For water: 3.34 X 10 5 J/kg

Fusion vs. Vaporization Heat of vaporization- Amount of thermal energy needed to change 1 kg of a liquid to a gas (vapor) or vice versa –For water: 2.26 X 10 6 J/kg Heat of vaporization- Amount of thermal energy needed to change 1 kg of a liquid to a gas (vapor) or vice versa –For water: 2.26 X 10 6 J/kg

Energy change in a single substance How much energy is removed from 0.25 kg of steam at 150˚C when it is changed to water at 50˚C? Energy to cool steam Q = m c Δ T Energy to change steam to water Q = m hv Energy to cool water Q = m c Δ T.25(2020)(50).25(2,260,000).25(4180)(50)