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 bowKinetic 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 startedex: 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 oF = freezing point of water

212 oF = Boiling point of water

oF = (oC 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 = -273.15 oC- Conversion:

- K = oC + 273- oC = 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 1oC

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∆TWhere: Q = heat (either lost or absorbed)

unit = Joule or caloriem = mass of substance

unit = gramC = specific heat of the substance

unit = J/g.oC or cal/g.oC∆T = change in temperature

unit = oC

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

Q = mC∆T

Ex: How much heat (J) is needed to raise 138.0g of water at 18.0 oC to 75.0 oC?

Q = mC∆T

Ex: How much heat was lost as 458.0g of water was cooled from 50.0 oC to 15.0oC?

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?

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?

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/gHeat 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 = 101.3 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 - 760

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 oC –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 phaseie: 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

http://www.kentchemistry.com/links/Matter/HeatingCurve.htm

Heating Curves

Heat of Vaporization – amount of energy needed to vaporize a mass of liquid at a given temperature

Q = mHvwhere: 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 = mHfwhere: 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 oC to 118 oC?

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

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

Phase Diagram

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

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 0C

Normal Boiling Point – boiling point of a substance at standard pressure (ex: 1 atm or 760 mmHg)

Water’s Normal BP = 100 oC

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