Changes in the state of matter Phase Changes

State of matter change triangle

Change in a material’s states of matter Is a Physical, not Chemical change No Chemical reaction occurs Done by adding or subtracting energy to the amount held by each atom Also called a phase change

When state of matter changes What does not change: The composition of the matter The mass (same mass of liquid water as steam)

When state of matter changes What does change: The volume of the matter The amount of energy held within the matter

Phase change Categories

Endothermic change Occurs when object gains energy from other sources Added energy result in less restrictive connections between atoms, molecules Types of endothermic change Melting Evaporation or boiling Sublimation

Exothermic change Occurs when an object loses energy to other objects or the environment Results in more restrictive connections between atoms Types of exothermic change: Freezing Condensation Deposition (sublimation)

Energy transfers associated with water Energy released to solidify into ice Energy absorbed to liquefy into water Energy released to condense into liquid Energy absorbed to vaporize into a gas

Making Smores Which material involved with making a smore undergoes a phase change? Endo or Exo changes?

Fire Heat from an outside source must be applied to the combustable material to make it burn (endothermic action) The products(hot air, ash) released from the chemical reaction have an increased amount of heat (endo) These products lose their heat as the move away from the source of the reaction (exothermic) The surrounding environment (air, the ring of rocks that border the fire, the marshmallow, you) become hotter as energy is transferred to you from the products of the fire

More examples of Exothermic Changes

Condensation Convert from gas to liquid Dew, the ‘sweating’ of cold bottles on hot summer days

Condensation: molecules have to slow down

condensation Look at the glasses During the summer

Exothermic Change of State

Can you think of any other examples of condensation?

Freezing Convert from liquid to solid Making ice cubes The cooling of molten lava to rock

Solidification

Freezing? What will freeze in this picture in time?

Deposition (sometimes called sublimation as well) Gas to solid without turning into a liquid Frost on the ground

Frost on ground

Where else does freezing occur

More examples of Endothermic Change

Evaporation, Boiling Convert from liquid to gas The drying up of lakes and ponds during the summer Boiling water in a pan

Evaporation of water at the salt flats: energy is transferred to the water molecules from the sun

melting Convert from solid to liquid Making Iron or Titanium a chocolate bar left out on blacktop

Melting What loses energy? What gains energy?

Melting of Titanium into ingots

Where is the energy coming from to melt or sublimate the ice?

Sublimation Direct change from solid to a gas Other examples: Freeze-dried food (coffee) Ice Cubes getting smaller in freezer Freezer-burn (too long, improperly wrapped)

Sublimation Dry Ice – solid carbon Dioxide

Sweating

Which phase changes are connected with sweating?

As you sweat, energy is transferred from your body to the water/oil droplets

Sweating Exercising increases the energy in your body Some of that energy is transferred to the molecules of water and oil that make up your sweat. Those water/oil molecule move through pores, evaporate when no longer confined inside the body, taking heat with them The transfer of that heat helps your body cool off

Example Sweating: You lose energy (exothermic) Sweat gains energy (endothermic) Energy has been transferred, not created or destroyed You feel cooler Sweat goes from liquid to gas (boiling, evaporation)

Temperature and phase change When substance gains or loses energy, either its temperature or its phase will change, but not both at the same time When adding heat to ice, temp will not rise until all ice has melted

Conservation of mass and energy In a closed environment: Mass can not be created or destroyed Energy can not be created or destroyed If some atom/molecule gains energy in some form, another must lose energy in some form

Conservation of a system The amount of mass or energy in a closed system remains constant, but can be rearranged or transformed

Closed System A closed system is a collection of objects that can transfer energy, mass only between themselves There is no gain or loss of energy, mass from a closed system

Extras

Refrigerators The refrigerant in the coils at the back of the refrigerator take out energy from air inside the refrigerator. Refrigerant evaporates inside coils Gas flows to outside of refrigerator, releases heat to environment, refrigerant condenses

Air Conditioners, Heaters

Air Conditioner Hot, humid air is sucked in from the room Heat is extracted from air and transferred to water in piping The cool dry air is recycled back into room Water condenses inside the air conditioner A fan takes the heat from the water and blows it away from unit outside of home