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) Law of Conservation of Energy - Energy can not be created nor destroyed - total energy before and after a reaction must be the same

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

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

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

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

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 = o C - Conversion: - K = o C o C = K - 273

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 1 o C

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

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

Calorimetry

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. o C or cal/g. o C ∆T = change in temperature unit = o C

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. o C or J/g. o C

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

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

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 o C?

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

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

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 = kPa = 760 torr

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

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

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 mmHg or 1atm

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

Measuring Pressure Closed Tube Manometer

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

Boiling and Melting Water boils at 100 o C –NOT NECESSARILY TRUE - Depends on the atmospheric pressure - Less pressure – boils faster - Ex: baking recipes in high altitudes

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)

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

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

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

Generic Heating Curve

Heating Curve Diagram  Curve.htm Curve.htm

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

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

How much heat is needed to raise 15g of water from 35.8 o C to 118 o C?

How much heat is needed to raise 25g of water from o C to 434 o C?

Phase Diagram

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

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 0 C Normal Boiling Point – boiling point of a substance at standard pressure (ex: 1 atm or 760 mmHg) Water’s Normal BP = 100 o C

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

Vapor Pressure Curve