Chemical Changes, Physical Changes and Mixtures

Physical Science

Chemical Change

when the chemical composition of a substance is altered

What is the rule when balancing this equation going through a chemical change?

C₃H₈ + 5O_{2 —>} 3CO₂ + 4H₂O

due to the rule of conservation of matter (matter cannot be created or destroyed), everything on one side of the equation has to be on the other side as well, but can be bonded differently

In this equation, what does the 3 apply to, and what does the ₂ apply to?

3CO₂

The 3 applies to carbon and oxygen, the subscript, 2 only applies to the oxygen

How many oxygen atoms are here?

5O₂

2×5=10

Balance this equation:

N₂+H₂ —> NH₃

N₂+3H₂ —> 2NH₃

Mixture

a material that can be separated by physical means into two or more substances

made by combining two or more different materials without a chemical reaction occurring (the objects do not bond together)

homogeneous or heterogeneous

Solution

a homogeneous mixture in which one substance has dissolved into the other(s)

ie: saline/salt water

Suspension

a system in which small particles are kept dispersed by agitation or molecular motion in the surrounding medium

ie: mud in water

physical change

a change from one state to the other without a change in chemical composition (ie solid, liquid, gas)

solid

coldest state, cannot be compressed (change volume), does not take shape of container

liquid

cannot be compressed, does take shape of container

gas

can be compresses, does take shape of container

Every substance has its own unique ______ and ______ ______.

boiling and freezing point

What are the two factors that cause a substance to change state?

temperature and pressure (altitude change)

The higher the altitude, the more/less pressure

less

therefore, for example, at sea level water boils at 212 degrees F but in the mountains with less pressure (less atmosphere pushing down) it boils at 210 degrees F

The more pressure, the more it wants to ______.

The less pressure, the more it wants to _______.

more: be a solid

less: be a gas

Charles’ Law

as the temperature goes up, so does the volume and vice versa

ex: rattling lid on a pot of boiling water

Boyle’s Law

as the pressure goes up, the volume goes down and vice versa

ex: a balloon shrinks in the pool if you swim down to the deep end with it

ex: if a balloon floats into the air, it will get bigger as the volume will increase until it eventually pops

pH

a measure of the presence of hydrogen ions in a substance/a measure of the acidity or basicity of a solution

it effects its tendency to bond with other substances

litmus

a water-soluble mixture of different dyes extracted from lichens.

Litmus Test

how pH is measured.

blue litmus paper turns red under acidic conditions

red litmus paper turns blue under basic (ie alkaline) conditions

What kinds of substances are usually alkaline?

most cleansers (ie soap, ammonia, lye)

What kinds of substances are usually acidic?

most foods (lemon juice, vinegar)

What is the neutral substance and what number is it at?

water, 7