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Heat, Energy and Phases of Matter

Heat, Energy and Phases of Matter. Energy – ability to do work Work - force x distance Two types of energy Potential Energy – stored energy ex: stretched bow Kinetic Energy – energy in motion ex: swinging a bat. Energy. Joule - SI unit for measuring energy (J)

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Heat, Energy and Phases of Matter

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  1. Heat, Energy and Phases of Matter • Energy – ability to do work • Work - force x distance • Two types of energy • Potential Energy – stored energy • ex: stretched bow Kinetic Energy – energy in motion ex: swinging a bat

  2. Energy Joule - SI unit for measuring energy (J) Law of Conservation of Energy - Energy can not be created nor destroyed - total energy before and after a reaction must be the same

  3. Energy and Chemical Reactions Endothermic - absorption of heat energy in a chemical reaction - increase in potential energy Exothermic – release of heat energy in a chemical reaction - decrease in potential energy

  4. Energy and Chemical Reactions Activation Energy - initial input of energy needed to get a reaction started ex: striking a match – provides frictional heat

  5. Heat Energy and Temperature Thermometers are based on the principle of expanding liquid Celsius Scale – is what our thermometers measure in 0 oC = freezing point of water 100 oC = boiling point of water

  6. Heat Energy and Temperature Fahrenheit Scale - not part of the SI system • Is what our weather is measured in. 32 oF = freezing point of water 212 oF= Boiling point of water oF = (oC x 1.8) + 32

  7. Heat Energy and Temperature Kelvin Scale – absolute zero represents the theoretical lowest possible temperature - absolute zero has yet to be reached • Unit = K • Absolute zero = -273.15 oC • Conversion: • K = oC + 273 • oC = K - 273

  8. Heat and It’s Measurement Calorie – non-SI unit to measure quantity of heat - quantity of heat that will increase the temperature of 1 gram of water by 1oC

  9. Calorimetry Measurement of the amount of heat released or absorbed during a chemical reaction Instrument used to measure this heat is called a Calorimeter

  10. Calorimetry Reaction occurs inside a reaction chamber surrounded by an unknown mass of water - heat released – enters the water and raises its temperature - Heat absorbed – lowers the temperature of the water

  11. Calorimetry

  12. Calculating Heat Q = mC∆T Where: Q = heat (either lost or absorbed) unit = Joule or calorie m = mass of substance unit = gram C = specific heat of the substance unit = J/g.oC or cal/g.oC ∆T = change in temperature unit = oC

  13. Calculating Heat Specific Heat – amount of heat energy required to raise the temperature of 1gram of a substance by 1 degree Celsius C for water = 1 cal/g.oC or 4.184 J/g.oC

  14. Q = mC∆T Ex: How much heat (J) is needed to raise 138.0g of water at 18.0 oC to 75.0 oC?

  15. Q = mC∆T Ex: How much heat was lost as 458.0g of water was cooled from 50.0 oC to 15.0oC?

  16. Q = mC∆T Ex: What is the final temperature of 15.0g of water if 238J of heat were added when it was 8.0 oC?

  17. Q = mC∆T Ex: A piece of unknown metal with a mass of 23.8g is heated to 100.0 oC and dropped into 50.0 ml of water at 24.0 oC. The final temperature of the system is 32.5 oC. What is the specific heat of the metal?

  18. Phase Changes • During a phase change, we use this formula: • Q = mass X heat of fusion (of heat of vaporization) Heat of fusion for water = 333 j/g Heat of vaporization = 2260 J/g

  19. Phases of Matter Pressure - force exerted on one unit area - SI unit = Newton (N) - other units – atm, torr, mm Hg, psi, and kPa equalities 1 atm = 760 mm Hg = 101.3 kPa = 760 torr

  20. Pressure Liquid pressure – exerted equally in all directions - swimmers feel an increase in pressure as they go deeper down into the ocean

  21. Pressure Atmospheric Pressure – (air pressure, barometric pressure) - at sea level, air pressure = weight of a kg mass on every square centimeter of surface exposed to it ** we are not conscious of air pressure because it is exerted in all directions

  22. Measuring Pressure Hg Barometer – measures AIR PRESSURE • Pressure varies with altitude • Decrease in air pressure as you increase altitude • Drop in air pressure before a storm • Normal Atmospheric Pressure - 760 mmHg or 1atm

  23. Measuring Pressure Manometer – measures pressure exerted by a gas in a closed container - 2 types – closed and open

  24. Measuring Pressure Closed Tube Manometer

  25. Phase Changes As a substance is heated, the particles gain energy, vibrate farther and farther apart, until they have enough energy to break out from the fixed pattern and enter a new phase

  26. Boiling and Melting Water boils at 100 oC –NOT NECESSARILY TRUE • Depends on the atmospheric pressure • Less pressure – boils faster • Ex: baking recipes in high altitudes

  27. Boiling and Melting Boiling Point - Temperature at which a substance changes from a liquid to a gas Melting/Freezing Point - temperature at which a substance changes from a solid to a liquid (melting) or from a liquid to a solid (freezing)

  28. Other phase changes Evaporation – process by which liquid water enters the gas phase Condensation – (reverse of evaporation) process by which a gas is cooled from above the boiling point

  29. Other Phase Changes Sublimation – process by which a solid changes directly to a gas without passing through the liquid phase ie: moth balls, dry ice, iodine

  30. Heating Curve Diagram • Temperature – Energy graph that describes the way a substance absorbs heat as it moves from the solid to liquid to gas states

  31. Generic Heating Curve

  32. Heating Curve Diagram • http://www.kentchemistry.com/links/Matter/HeatingCurve.htm

  33. Heating Curves Heat of Vaporization – amount of energy needed to vaporize a mass of liquid at a given temperature Q = mHv where: m = mass (g) Hv = enthalpy of heat = constant value = Hv for water = 2260 J/g

  34. Heating Curves Heat of Fusion – heat needed to change a mass of solid to a liquid at a given temperature Q = mHf where: m = mass (g) Hf = enthalpy of fusion = constant value = Hf for water = 334 J/g

  35. How much heat is needed to raise 15g of water from 35.8 oC to 118 oC?

  36. How much heat is needed to raise 25g of water from -24.5 oC to 434 oC?

  37. http://www.dlt.ncssm.edu/TIGER/Flash/phase/HeatingCurve.html

  38. Phase Diagram http://www.youtube.com/watch?v=zSwG59d8OCc

  39. Phase Diagram Triple Point – point at which all three phases can coexist Critical Point – Point at which a substance can no longer exist as a liquid regardless of the temp. or pressure

  40. Phase Diagram Normal Melting/Freezing Point – melting/freezing point of a substance at standard pressure (ex: 1 atm or 760 mmHg) Water’s Normal MP = 0 0C Normal Boiling Point – boiling point of a substance at standard pressure (ex: 1 atm or 760 mmHg) Water’s Normal BP = 100 oC

  41. Vapor Pressure Pressure of a vapor in equilibrium with its liquid - in a container equilibrium is reached when the space above the liquid holds as much vapor as it can (saturated) - as temperature of a liquid increases, the liquids vapor pressure increases - when the vapor pressure = atmospheric pressure, the liquid begins to boil ****Heating of a boiling liquid DOES NOT raise its temperature

  42. Vapor Pressure Curve

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