Chemistry CPE: Midterms - Lee

Chemistry (definition)

Study of the composition, structure, and properties of matter; the processes matter undergoes; and the energy changes that accompany those processes

Matter

Anything that has mass and takes up space (volume)

Example of matter

Water, air, rock, metal, saltwater

Not matter (in your notes)

Light

Chemical

A substance with a definite composition (same makeup everywhere)

Example of a chemical

CO₂, H₂O, C₆H₁₂O₆

Pure substance

Made of one kind of building block; definite composition; not a mixture

Mixture

Contains more than one substance; can often be separated physically

Element

Pure substance made of one type of atom; cannot be broken down chemically

Compound

Two or more different elements chemically bonded in fixed ratios

Building block of an element

Atom

Building block of a compound

Molecule (chemically bonded atoms)

Homogeneous mixture (solution)

Uniform throughout; same composition everywhere

Heterogeneous mixture

Not uniform; different parts visible

Example homogeneous mixture

Air, saltwater, Kool-Aid

Example heterogeneous mixture

Salad, trail mix, sand + water

Physical separation method: filtration + evaporation

Filter solid out, then evaporate liquid to leave dissolved solid

Distillation

Separates liquids by different boiling points

Physical property

Observed/measured without changing substance identity

Chemical property

Describes ability to change into different substances

Examples of physical properties

Color, density, melting point, boiling point, state of matter, solubility

Examples of chemical properties

Flammability, rusting/reactivity with oxygen, reactivity with acids, tarnishing, corrosiveness

Intensive property

Does not depend on amount of matter present

Extensive property

Depends on amount of matter present

Examples of intensive properties

Density, boiling point, melting point, color, temperature

Examples of extensive properties

Mass, volume, length, total energy

Physical change

Change that does not alter identity of substance

Chemical change

Change that forms new substances

Examples of physical changes

Melting ice, boiling water, cutting paper, dissolving sugar in water

Examples of chemical changes

Burning wood, rusting iron, baking a cake, digestion

Signs of chemical change

Gas produced, precipitate formed, color change, energy change (heat/light)

Solid (particle description)

Particles tightly packed, vibrate in fixed positions; definite shape and volume

Liquid (particle description)

Particles close, slide past each other; definite volume, no definite shape

Gas (particle description)

Particles far apart, move quickly; no definite shape or volume

Endothermic phase change

Energy absorbed (melting, boiling)

Exothermic phase change

Energy released (freezing, condensation)

Law of Conservation of Mass

Mass is neither created nor destroyed; mass of reactants = mass of products

Law of Conservation of Mass (equation idea)

Total mass before reaction = total mass after reaction

Periodic table groups (columns) significance

Elements in the same group have similar chemical properties

Metals (location + properties)

Left/center; shiny, malleable; good conductors of heat/electricity

Nonmetals (location + properties)

Upper right; poor conductors; many gases; brittle solids

Metalloids (location + properties)

Stair-step border; properties between metals and nonmetals

Scientific method

Observe, ask question, form hypothesis, experiment, analyze results/conclude; theories supported by data

Hypothesis

Testable prediction/educated guess that can be supported or rejected

Qualitative data

Descriptive data using words (color, smell)

Quantitative data

Numerical data using numbers and units (25 g, 20°C)

Controlled experiment

Tests one independent variable while keeping all other conditions constant

Independent variable (IV)

Factor you change/test

Dependent variable (DV)

Outcome you measure

Constants

Factors kept the same throughout the experiment

Control group/setup

Group that does not receive the experimental treatment/IV

Experimental group/setup

Group that receives the independent variable/treatment

Quantity (in measurement)

Something measured with a number and a unit

SI base unit for length

meter (m)

SI base unit for mass

kilogram (kg)

SI base unit for temperature

kelvin (K)

SI base unit for time

second (s)

SI base unit for amount of substance

mole (mol)

Derived unit: area

m²

Derived unit: volume

m³ (also commonly L or mL in chemistry)

Derived unit: density

mass ÷ volume (g/mL or g/cm³)

Density formula

D = m ÷ V

Mass (definition)

Amount of matter in an object (often in grams)

Volume (definition)

Amount of space an object occupies (often in mL or cm³)

Metric prefix kilo (k)

10³ = 1,000

Metric prefix hecto (h)

10² = 100

Metric prefix deka (da)

10¹ = 10

Metric base unit prefix

10⁰ = 1

Metric prefix deci (d)

10⁻¹ = 0.1

Metric prefix centi (c)

10⁻² = 0.01

Metric prefix milli (m)

10⁻³ = 0.001

Metric prefix micro (μ)

10⁻⁶ = 0.000001

Metric prefix nano (n)

10⁻⁹

Metric prefix pico (p)

10⁻¹²

Metric prefix mega (M)

10⁶ = 1,000,000

Metric equality: kilometers to meters

1 km = 1000 m

Metric equality: meters to centimeters

1 m = 100 cm

Metric equality: centimeters to millimeters

1 cm = 10 mm

Metric equality: liters to milliliters

1 L = 1000 mL

Metric equality: grams to milligrams

1 g = 1000 mg

Dimensional analysis (factor-label)

Multiply by conversion factors so unwanted units cancel

Dimensional analysis step 1

Write the given value with units

Dimensional analysis step 2

Multiply by conversion factors (ratios equal to 1)

Dimensional analysis step 3

Cancel units and solve

Across-systems conversion factor (given in notes)

1 inch = 2.54 cm

Accuracy

How close a measurement is to the true/accepted value

Precision

How close repeated measurements are to each other

Significant figures (purpose)

Show how precise a measurement/value is

Sig fig rule: nonzero digits

Always significant

Sig fig rule: zeros between nonzero digits

Significant

Sig fig rule: leading zeros

Not significant

Sig fig rule: trailing zeros with a decimal

Significant

Sig fig rule: trailing zeros without a decimal

Not counted unless shown/indicated

Atlantic–Pacific rule (sig figs)

Decimal present: start left at first nonzero; Decimal absent: start right at first nonzero

Rounding for addition/subtraction

Round to the fewest decimal places

Rounding for multiplication/division

Round to the fewest significant figures

Rounding rule (timing)

Round at the end (don’t round early)

Scientific notation form

M × 10ⁿ where 1 ≤ M < 10 and n is an integer

Standard

scientific notation (direction)

Scientific notation exponent (move left)

Positive exponent