UNIT 2 – MATTER AND CHANGE

Conceptual Chemistry

Objective 1

Read and express information given in chemical formulas.

What is matter?

Matter: Anything that has mass and takes up space.

Pure Substances

Matter that has fixed composition and properties.

Cannot be broken down by physical methods.

Elements

A substance that cannot be broken down by chemical means.

i.e. iron (Fe), carbon (C), oxygen (O), nitrogen (N)

Compounds

A substance made of elements that are chemically combined.

i.e. water (H2O), salt (NaCl), sugar (C12H22O11)

Compounds

Every compound is composed of the elements it contains.

Chemical Formula

Shows the type and number of atoms present in a substance.

Chemical Formula

• In the chemical formula, subscripts show how many atoms are in the compound.

C6H10N2O2

C = 6H= 10N= 2O= 2

Chemical Formula

The large numbers in front of the chemical formula, called coefficients, show the number of particles.

3C6H10N2O2

C6H10N2O2 = 3 total

Practice Problems: How atoms of each element are in the following?

1. CH4

2. AlCl3

3. 4 H2O

4. 10 Fe3P2

5. 6 Zn(NO3)2

6. Al2(SO3)3

Objective 2

Classify matter as a pure substance or a mixture.

Mixtures

Matter that has compositions that are not uniform or definite.

Mixtures

Mixtures can be separated by physical means into the substances that are mixed with in them.

Homogeneous Mixtures

Homo = same The composition is the same

throughout

Examples Solid Solid: Brass

(Zinc and Copper)

Liquid Liquid: Alcohol (Ethanol and Water)

Gas Gas: Air (Nitrogen and Oxygen)

Solid (dissolves) Liquid: Salt Water (Sodium Chloride and Water)

Gas (dissolves) Liquid: Carbonation (Carbon Dioxide and Water)

Heterogeneous Mixture

Hetero = different The composition is different

throughout.

Objective 3

Distinguish between chemical and physical changes, as well as chemical and physical properties.

Practice ProblemsHetero or Homo Mixture Why?

Tap Water :_______________

A Rock: ________________

Stainless Steel:________________

Brewed Coffee: ________________

Sand: ________________

Oatmeal: ________________

Dust Free Air: ________________

Rusty Metal: _________________

Properties of Matter

Physical Properties: Can be measured without changing the substance’s chemical composition.

  i.e. melting point, boiling point, density, solubility,

odor, hardness, color, etc.

Chemical Properties: Potential reactivity of substance with other substances. Can only be measured by trying the reactions.

i.e. Any particular reaction a substance undergoes.

Changes of Matter

Physical Change Chemical Change

Physical Change

Alters a substance without changing the substance’s chemical composition.

i.e. melting, boiling, cutting, smashing, dissolving

 

Chemical Change

Occur when one or more substances are changed into another substance that have different chemical compositions.

i.e. rusting, exploding, decomposing, corroding, spoiling

 

Practice ProblemsChemical or Physical

Property?Chemical or Physical Change?

Tarnishes in Rain: Lighting a firework:

Bends easily: Boiling Pasta:

Decomposes: Chewing gum:

Reusable/Recyclable: Running your car:

Shiny: Rolling your bike:

Not Flammable: Melting a crayon:

Perishable Food: Rusting a nail:

Freezable Food: Opening a can of pop:

Objective 4

Balancing chemical equations.

Chemical Equation

Ex: 2 KClO3 2 KCl + 3 O2

Describes the original beginning substances (called reactants) using chemical formulas. Then an arrow points to the newly created substances (called products) using chemical formulas again.

Reactants Products

Symbols

(s) = (l) = (g) = (aq) =

+ =  = ∆ = H2 (subscripts) =

 2 H2 = (Coefficients) =

Balancing Equations

The law of conservation of mass states that matter cannot be created or destroyed. So, the number of atoms reacting must equal the number of atoms produced. However, a chemical change rearranges these atoms into new substances.

To balance equations, follow these steps:

1. Count atoms on each side of the arrow. They should be equal. If not, you need to balance them.

2. Balance both sides by using coefficients. Remember, they multiply through everything inside of that compound. NEVER change subscripts.

3. Double check work.

Practice Problems

____ KClO3 ____ KCl + ____ O2

____AlBr3 + ____ K2SO4 ____ KBr + ____ Al2(SO4)3

____ C3H8 + ____ O2 ____ CO2 + ____ H2O

Objective 5

Describing chemical reactions and calculate percent yield and percent error.

Error Calculations

Error = experimental value – accepted value

Magnitude of the value tells whether or not the experimental value is too high or too low

Accepted value: Accurate value based on a reliable reference

Experimental value: value measured in lab

Percent Error = | Error | x 100%

Accepted Value

Percent Yield

Used to determine completeness of a reaction

Actual Yield: actual amount of products produced in an experiment

Theoretical Yield: maximum amount of products predicted from conservation of mass

Percent Yield = Actual Yield x 100%

Theoretical Yield