Matter and Energy Matter and energy interact and cause changes in matter (Chemical or Physical).

Energy Definition: the ability to do work Is NOT matter Is measured in the unit Joules (J) (See Table D) Can be POTENTIAL or KINETIC

Potential Energy Energy that is stored (i.e. in a chemical bond). Something has the “potential” to do some kind of work Example: the child at the top of the slide has potential energy

Kinetic Energy Energy of motion Example: the child going down the slide now has kinetic energy

So why do we want to study energy? Energy = the ability to do work! Having something do work is great! Examples: our bodies need energy to do work, our cars rely on energy to do work, our homes need to be heated via energy, etc…

Different types of energy… Light  is waves, visible or invisible Electrical involves moving electrons Heat movement of molecules Chemical is contained in foods Nuclear responsible for the sun Sound waves/vibrations of molecules Mechanical involves moving objects Magnetic opposing poles

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

Light Responsible for colors Responsible for sight We have found ways to use light to improve how much we can see and what we see (example: TV) Caused by electrons giving off energy

Chemical and Electrical Energy Energizes everything from remote controls to cars. Batteries convert chemical energy into electrical energy.

Chemical Energy Chemical energy from crude oil (natural, non-renewable resources) is used to heat our homes and run factories that produce consumer goods. Burning oil converts chemical energy into thermal energy.

Examples of Conservation of Energy When you watch TV, it starts as electrical energy and converts to radiant and sound energy. The radiant energy (or light energy) goes into your eye and converts to electrical energy in your nerves and then to the brain. The sound energy (vibrations) go to your ear drum where is vibrates sending electrical impulses to the brain.

Summary: What will we study in this unit? What is heat? How is it different from temperature? How does energy relate to chemical reactions (chemical change)? How energy relates to phase changes (physical change)?

Understanding Heat Flow Heat (q) is defined as the energy that transfers from one object to another. Heat flows from warm  cool. Describe the heat flow if a piece of iron with a temperature of 100oC was placed in a beaker of water at 50oC.

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 (together they make the universe). Exothermic Changes (think heat out): The system loses energy the surroundings absorbs energy Endothermic Changes (think heat in): The system absorbs energy from the surroundings

Exothermic Reactions (Chemical Changes) Exothermic reactions RELEASE ENERGY (i.e. explosions). A good way to remember this is to associate “EXO” with “OUT”. Has a –q value because heat is leaving the system. Heat is a product.

Endothermic Reactions (Chemical Changes) Endothermic reactions ABSORB ENERGY A good way to remember this is to associate “ENDO” with “INSIDE”. Has a +q value because heating is entering the system. Heat is a reactant.

Activation Energy Sometimes reactions can’t occur on their own (they can be exothermic). They need a little input of energy to get it started. This energy is called ACTIVATION ENERGY. Can you think of a common example of a reaction that requires activation energy?

Energy and Phase Changes Energy of particles of matter relates to the phase or state of matter (solid, liquid, or gas) Therefore, changes in energy can result in physical changes of matter. Let’s review what we should already know…

States or Phases of Matter Review Solid (s) Definite Shape and Volume Particles very tightly packed neatly arranged Not Compressible Liquid (l) Definite Volume only Particles are slightly spread apart and random Gas (g) No definite shape or volume Particles are very far apart and random Compressible

States or Phases of Matter Review

Phase Changes Other terms Change in phase Endo or Exo (thermic) Sign of ΔH or q (change in heat) Melting Liquefying S  L Endo + Freezing Solidifying L S Exo - Vaporization (not evaporation) Boiling L  G Condensation _______ G  L Sublimation Deposition S  G G  S

Heating/Cooling Curve of Water

What changes in phase are occurring… AB- solid, ice BC- melting CD- liquid DE- boiling EF- gas

What changes in energy are occurring… When heating or cooling a substance Kinetic Energy changes mean changes in the speed of the particles (temperature changes constant phase). Potential Energy changes mean changes in the relative distance of the particles (constant temperature phase change)

Changes in Energy AB- increase in KE (as evident by increase in temperature) no change in PE BC- no change in KE, but continually adding heat, so increase in PE CD- increase in KE DE- increase in PE EF- increase in KE

Cooling vs. Heating Cooling Curve goes down Heating Curve goes up

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 kinetic energy of the particles increases, temperature increases and the particles move faster. When phase changes occur the heat is being absorbed/released as potential energy and the distance of the particles change.

What is specific heat capacity (C) ? The amount of heat energy required to raise 1 unit of mass of a substance by 1 unit temperature. Symbol = C C=4.18 J/g°C (specific heat capacity of water). Table B

Specific Heat Capacity(C) & Heating/Cooling Curves On a Heating/Cooling curve the specific heat capacity is represented by the segments that have a temperature change.

Heat of Fusion Heat of fusion = amount of heat energy absorbed or released when melting or freezing. Symbol = Hf See Reference Table B for values Ex: Hf H2O = 334 J/g

Heat of Fusion & Heating (Hf) and Cooling Curves The heat of fusion (Hf) on a Heating or Cooling Curve is represented by the constant segment in between the solid and liquid phase.

Heat of Vaporization Heat of vaporization = heat absorbed or released when vaporizing or condensing. Symbol = Hv See Reference Tables for values. Ex: HVH2O = 2260 J/g

Heat of Vaporization & Heating (Hv) and Cooling Curves The heat of vaporization (Hv) on a Heating or Cooling Curve is represented by the constant segment in between the liquid and gas phase.

Comparing Fusion and Vaporization On a Heating Curve the segment for vaporization is typically longer than the segment for fusion. Why do you think that is? DE is longer than BC???? It takes more energy to boil a substance than it does to melt a substance. More time = more energy

Heat Calculations and Phase Changes One can calculate how much heat is absorbed or released during temperature changes and phase changes.

If the problem says… Potential energy Melt/freeze Vaporize condense At 0°C (melting/freezing point) At 100°C (boiling/condensing point) Potential energy Use Q = mHf (melting/freezing) or Q = mHv (vaporization/condensation)

If the problem says… Kinetic energy (calorimetry) Temperature changes Increase in temp from __ to __ Decrease in temp from __ to __ Heat a liquid/solid Cool a liquid/solid Kinetic energy (calorimetry) Use Q = mCΔT

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. To calculate the amount of heat absorbed or released use the q=mC∆T equation and calculate the heat change of water.

Cheap Calorimeter- insulation

Example: A reaction takes place in a calorimeter containing 400.0 g of water at an initial temperature of 22.5oC. The temperature of the water decreases to 17.0oC. How much heat energy was absorbed by the reaction?

Example: A substance undergoes combustion in a calorimeter and the following data are obtained: Mass of water in calorimeter: 102.8 g Initial temperature of water: 24.0oC Final temperature of water: 73.1oC Based on the data above calculate the amount of heat energy released during the combustion reaction that took place?