Matter and Energy

When Matter and energy interact changes in matter occur.

Energy

Definition: the ability to do workIs NOT matterIs measured in the unit Joules (J)Can be POTENTIAL or KINETIC

Potential EnergyEnergy that is storedSomething has the “potential” to do some kind of workExample: the child at the top of the slide has potential energy

Kinetic Energy

Energy of motionExample: the child going down the slide now has kinetic energy

Different types of energy…

Light is waves, visible or invisibleElectrical involves moving electronsHeat movement of moleculesChemical is contained in foodsNuclear responsible for the sunSound waves/vibrations of moleculesMechanical involves moving objectsMagnetic opposing poles

Law of Conservation of Energy

Energy, like matter, is neither created nor destroyed, rather it is converted.

Summary:What will we study in this unit?

What is heat? How is it different from temperature?How does energy relate to chemical reactions? How energy relates to phase changes?

Understanding Heat Flow

Heat (q) is defined as the energy that transfers from one object to another.

Heat flows from warm cool.

What will happen if the two objects are touching?

Heat Energy vs. Temperature

Temperature is measure of the heat flow.

Temperature is a measure of the average kinetic energy of the particles in matter.

Heat Energy and Changes in Matter

In virtually all changes in matter, energy is released or absorbed.

System vs. Surroundings

Examples

Exothermic Reactions (Changes)

Exothermic reactions RELEASE ENERGY

Has a Negative q value.

Heat is a product.

Endothermic Reactions (Changes)

Endothermic reactions ABSORB ENERGY

Has a Positive q value because heat is entering the system.

Heat is a reactant.

Activation Energy

Sometimes reactions can’t occur on their own

They need a little input of energy to get it started.

This energy is called ACTIVATION ENERGY.

Energy and Phase Changes

Energy of particles of matter relates to the phase or state of matter (solid, liquid, or gas)

Changes in energy then result in changes of matter.

Phase ChangesOther terms

Change in phase

Endo or Exo

Sign of ΔH or q

Melting Liquefying

S L Endo +

Freezing Solidifying

L S Exo -

Vaporization Boiling L G Endo +

Condensation

_______ G L Exo -

Sublimation _______ S G Endo +

Heating Curve of Water

A

B C

D

E

F

What changes in phase are occurring…

AB- solid, iceBC- meltingCD- liquidDE- boilingEF- gas

What changes in energy are occurring…

AB- increase in KEBC- no change in KE, but still adding heat, so increase in PECD- increase in KEDE- increase in PEEF- increase in KE

What is specific heat capacity?

The amount of heat energy required to raise 1 unit of mass of a substance by 1 unit temperature.

C=4.18 J/g°C (specific heat capacity of water). Table B

Heat of Fusion

Heat of fusion (Hf) = amount of heat energy absorbed or released when melting or freezing.

See Reference Table B for valuesEx: Hf H2O = 334 J/g

Heat of Vaporization

Heat of vaporization = heat absorbed or released when vaporizing or condensing.

See Reference Tables for values.Ex: HVH2O = 2260 J/g

Kinetic Theory of Heat

Molecules and atoms are constantly in motion, even in the SOLID phase.

They are said to have kinetic energy or the energy of motion.

As the energy of the particles increases, temperature increases.

Heat Calculations and Phase Changes

One can calculate how much heat is absorbed or released.

If the problem says…

Melt/freezeVaporize condenseAt 0°C (melting/freezing point)At 100°C (boiling/condensing point)

Use

Q = mHf (melting/freezing) or

Q = mHv (vaporization/condensation)

Pote

nti

al

energ

y

If the problem says…

Temperature changesIncrease in temp from __ to __ Decrease in temp from __ to __Heat a liquid/solidCool a liquid/solid

Use

Q = mCΔTKin

eti

c energ

y

Examples

How much heat is needed to melt 10.5 grams of ice at 0°C?Use Q = mHf Q = (10.5 g) (334 J/g)Q= 3507 J

Examples

What mass of liquid water can be vaporized if 680 J of heat energy is added at 100°C?

Use Q = mHv 680 J = (m) (2260 J/g)m= 0.30 g

Examples

How much energy is needed to increase the temperature of 5.0 grams of water from 0°C to 10°C?

Use Q = mCΔT Q = (5.0 g) (4.18 J/g°C)(10-0)Q= 209 J

Examples

What is the mass of water that can be increased in temperature by 15°C by the addition of 800 J?

Use Q = mCΔT 800 J = (m) (4.18 J/g°C)(15°C)m= 12.8 g

Calorimetry

Used to measure amount of heat released or absorbed during a chemical/physical change that occurs in water solution.“calorimeter” is used to measure the change in temperature of water surrounding a reaction.

Cheap Calorimeter- insulation