Matter Notes Revised

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Physical and Chemical Changes

8.P.1.3

Changes in the properties of matter can be physical or

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Concept of Change

 Change: the act of altering a

substance

 Changes can be physical or chemical

 When considering what TYPE of

change has occurred…ask yourself:

 “Did the identity of the substance

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Physical Change

 Physical change: a change that occurs

that does not change the identity of the substance

 Melting ice

 Freezing Kool-aid  Tearing paper

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Review

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Special Physical Changes

 Melting point: the temperature at

which a substance changes from a solid to a liquid at a given pressure

water = 0oC

 Boiling point: the temperature at

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Density

 Density is the amount of mass per

unit of volume.

 Density can be used to identify a

substance.

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Specific Heat

_{A physical property because it does}

not change the substance

_{Definition: the amount of energy that}

is needed to raise the temperature of 1 kg of a substance 1 degree Celsius

_{Water has a high specific heat, which}

means it takes a lot of energy to raise its temperature and take longer to

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Solubility

_

By textbook definition: the measure of one substance’s ability to dissolve in a specific amount of another substance at a given temperature and pressure to form a solution

_{Comes from the word solution, in}

which two or more substances are mixed evenly together

_{For example: Sweat is a solution of}

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Conductivity

_{A physical property}

_{By textbook definition: the measure of}

the ease with which electrons move through a material

_{Means electricity can travel through} _{Good conductors are copper wiring,}

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Malleability

_{A physical property}

_{By definition: the ability of a material to}

be hammered or rolled into sheets

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Magnetism

• _{By textbook definition: the ability of a}

material to be attracted or repelled by another material due to a magnetic

field

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Specific Heat

_{A physical property because it does}

not change the substance

_{Definition: the amount of energy that}

is needed to raise the temperature of 1 kg of a substance 1 degree Celsius

_{Water has a high specific heat, which}

means it takes a lot of energy to raise its temperature and take longer to

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More on Specific Heat

 _{Remember: The specific heat of a substance} is the amount of heat (measured in joules, J) required to raise the temperature of 1 kg of a substance 1 degree Celsius.

 _{Water has a high specific heat, which means} it requires a lot of heat to raise its

temperature.

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Table 1, pg. 293

Specific Heat for Common Substances

Substance Specific Heat (J/kg degree Celsius)

Water 4180

Wood 1760

Iron (Fe) 450 Gold (Au) 129

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And more…Specific Heat

 _{That means, a substance with a low}

specific heat will get hotter faster!

 _{So, using the previous table, Gold will}

get hotter than Iron when exposed to the same amount of heat for the same amount of time.

 _{Wood will get hotter faster than water}

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Chemical Changes

 Chemical change: a change that

occurs causing the identity of the substance to change

 Burning paper  Digesting food

 Electrolysis of water

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Chemical Changes Cont’d

 Indicators of a chemical change:

• Evolution of light • Evolution of heat • Evolution of a gas • Color change

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Evidence of a chemical reaction

 _{precipitate is a solid that forms when}

two liquids react with each other.

 _{The precipitate is a product of the}

chemical reaction

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Catalyst

 _{A substance that can make something}

happen faster but is not changed itself

 _{speeds up a chemical reaction by}

providing a surface for the reaction to occur

 _{For example: catalysts are used in the}

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Temperature part 1

 _{Changes rate: if you lower or raise the}

temperature of an item you can change the rate of the reaction

 _{For example: if you put bread in the}

refrigerator it lowers the bread’s overall temperature and slows the bread’s

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Temperature part 2

• _{Affects the rate of reaction: the higher the temperature}

the faster the molecules in a substance moves; this typically increases the speed at which the chemical reaction will occur

• _{The molecules collide with each other much more often}

in higher temperatures which will separate the existing bonds between molecules (at higher temperatures)

• _{For example: baking a cake—started as a liquid}

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Gas Production

 _{The bubbles tell you a gas has been} produced

 _Reactant_{: substance that exist before the} reaction begins

 _Product_{: the substance formed as a} result of the reaction

 _A_{chemical equation}_{tells chemists at a} glance the reactants, products, physical state, and the proportions of each

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Table 1, pg. 383

Reactant Product

Baking Soda+Vinegar → Gas+White Solid Charcoal+Oxygen → Ash+Gas+Heat

Iron+Oxygen+Water → Rust

Silver+Hydrogen sulfide→ Black tarnish+gas Gas(Kitchen range)+Oxygen→Gas+Heat

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Common Chemicals

• _{Vinegar is acetic acid dissolved in water} • _{Baking soda is sodium bicarbonate}

• _{Combine the two and the chemical}

equation looks like:

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Chemical Equation for Baking Soda and

Vinegar using Chemical symbols

CH₃COOH+NaHCO₃→CH₃COONa+H₂O+ CO₂

Vinegar+baking

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Is it Physical or Chemical?

Change Physical Chemical

Melting cheese

Burning wood

Milk souring

Wadding up paper