Science AHSGE Standard II Objective 4- Physical and Chemical Changes.

Science AHSGE Standard II

Objective 4- Physical and Chemical Changes

The Law of Conservation of Matter

• Matter can neither be created nor destroyed, only transformed from one form to another– These transformations can be physical changes

or chemical changes

Physical Change

• A change in the appearance of a substance

• Still the same substance – Mixture- Physically

combining substances without altering either

• Can take back apart

• Solution- Mixture of a solute and solvent

– Solvent- Substance dissolving a solute

– Solute- Substance being dissolved in a solvent

• Typically, changes in the state of matter

• Brought on by a change in temperature

Physical Changes

• Freezing- Liquid to solid– Freezing point- temperature

at which a substance will freeze

• 0° Celsius; 32° Farenheit or below

• Melting- Solid to liquid– Melting point- temperature at

which a substance will melt• 0° Celsius; 32° Farenheit

or above

Physical Changes

• Evaporation- Liquid to gas– Boiling- Forced evaporation

by adding heat • Boiling point- Temperature at

which a substance will boil– 100° Celsius; 212° Fareinheit

Physical Changes

• Condensation- Gas to liquid– Due to temperature changes

– Ex: Water on windows in the morning

• Sublimation- Solid to gas– Ex: Moth balls, potpourri

Physical Changes

• Distillation- Change from a liquid to gas and back to a liquid– Purifies (cleans) liquid’

– Commonly done for water and alcoholic beverages

Chemical Changes

• A change in matter that results in a different substance

• Changes appearance and chemical properties

• Can not mechanically separate back to original substances

• Usually accompanied by a change in energy

• Often gives off heat and/or light

• Compounds- Chemically combined elements bonded together – Compounds can be separated

or built to form new substances

– Ex: 2H2O2H⃗ 2 + O2

• Water separates into hydrogen and oxygen gas or vice versa

Chemical Changes

• Combustion- Chemical process converting chemical energy into heat and light energy– Ex: Burning

– Anywhere there’s smoke, there’s combustion

– Anything that can burn has chemical energy

Chemical Changes

• Fermentation- Partial breakdown of a substance due to a lack of oxygen– Ex: Carbon dioxide

escaping fallen fruit, creating alcohol

Chemical Changes

• Electrolysis- Decomposition of a substance by use of electrical current– Ex: Breakdown of water by

attracting hydrogen and oxygen gas to opposite terminals of a battery

Rate of Reactions

• Inhibitor- Any substance that slows or stops a reaction

• Catalyst- Any substance that speeds up a reaction– Ex: Water speeds up the rusting

process water

• Iron + Oxygen Iron oxide (rust)⃗– Enzyme- Special type of catalyst

that lowers the activation energy required to start a reaction; starts faster

• Found in stomach and in cell lysosomes

• The greater the surface area of a substance, the faster it reacts– Smaller substances have greater

surface area than larger substances– Ex: Sugar grain will dissolve

faster than a sugar cube

• Increase in temperature, increases reaction rates

• Increase in concentration (amount) of solvents increases reaction rate

• Stirring or shaking increases reaction rate