Chemistry - CH.3 Key Concepts

Pure Substance

Substance composed of any one type of atom or molecule

• Has a constant composition

• Can be an element or compound

PS: Element

A substance that CANNOT be broken down into simpler substances

• All known elements on the periodic table

• Chemically REACTIVE and COMBINE with other elements to form compounds

PS: Compound

A pure substance composed of TWO OR MORE elements in FIXED, DEFINED proportions

• More common than pure elements

• Can be decomposed into SIMPLER substances

Mixture

Composed of 2+ different types of atoms or molecules that can be labeled as heterogenous and homogeneous.

• Can contain 2+ substances that are PHYSICALLY MIXED but NOT CHEMICALLY COMBINED

• Can be combined UNIFORMALY or UNEVENLY

M: Heterogeneous

Uneven distribution of 2+ substances

• Can be told apart

M: Homogeneous

Uniform properties throughout → 2+ substances are uniform

• Cannot be told apart

Matter

Anything that has mass and volume (Occupies space) → Dimensional

• EX: Solid, liquid, gas

Solid

Tightly packed particles of matter

• May vibrate at a fixed point, but do not move relative to each other

PROPERTIES:

• Definite shape and volume

• Proximate and rigid particles

• Vibrate slowly at fixed positions

Liquid

Loosely packed molecules

• Free to move past one another and in random directions

PROPERTIES:

1. Definite volume

2. Proximate and mobile particles

3. No set movement pattern → Random

4. Takes shape of container

Gas

Flexible and uniform particles that are far apart

• Take the shape of a container

PROPERTIES:

1. No definite shape or volume

2. Far apart particles

3. Fast moving particles with little attraction to each other

Physical Property

A substance that displays WITHOUT changing its chemical composition

• EX: Color, melting point, conductivity, and boiling point (tested without changing the chemical composition)

• - Change in state, appearance, shape, and size

Chemical Property

A reaction must occur upon interaction → A change in chemical composition

• EX: Reactivity with oxygen, combustibility, flammability…

• - Molecules are broken for molecules to interact, causing a change

Change of State: Solid and Liquid

Solid-to-Liquid: Melting → heat is added

Liquid-to-Solid: Freezing → heat is removed

Change of State: Liquid to Gas

Liquid-to-Gas: Vaporization → +Heat

Gas-to-Liquid: Condensation → -Heat

Change of State: Solid to Gas

Solid-to-Gas: Sublimation → +Heat

Gas-to-Solid: Deposition → -heat

Thermal Energy

The amount of motion in a substance

• - The unit of measurement for temperature → More heat increases motion in atoms and molecules

Heat

The transfer of thermal energy between two bodies at different temperatures

• - Contains its own units of energy

• EQUATION: Heat =( mass (m) x Delta-T ) x Specific Heat Capacity (C)

Celsius to Fahrenheit

9/5(C +32)

Fahrenheit to Celsius

5/9(F - 32)

Celsius to Kelvin

K = C +273

• - Kelvin avoids the negative temperature by assigning onto the coldest possible temperature

The Law of Conservation

States that energy is neither CREATED nor DESTROYED

• PROPERTIES:

• - Total amount of energy is constant

• - Energy can be charged from one form to another

• - Transformed from one object to another

• - CANNOT be created out of nothing nor vanish into nothing

Potential Energy

Energy stored for use at a later time

• - Determined by the position of an object or chemical composition of a substance

• EX: Chemical bonds in foods

Kinetic Energy

Matter in motion

• - Any moving object has kinetic energy

• EX: Water flowing over a dam or working out

Joule (J)

The S.I. unit of energy

- calories is a second measurement unit of energy

• 1. 1 cal = 4.184 J

• 2. 1kJ = 1×10³J

• 3. 1ucal = 1×10³cal

The Nutritional Calorie

The necessary amount of energy needed each day depends on factors like age, gender, and level of activity.

- Written with a capital “C” → labeled as the kilojoules (kJ)

• 1. 1 Cal = 1×10³ cal

• 2. 1 Cal = 1kCal

• 3. 1 Cal = 4184 J

• 4. 1 Cal = 4.184 kJ

Specific Heat Capacity

Specific Hear Capacity (C) = Heat (q) / mass(m) x Delta-T

• → In the S.I. system, the units are J/g x degrees Celsius

• → In the metric system, the units are cal/ g x degrees Celsius

How is the movement of heat calculated?

The amount of heat lost or gained by a substance is concluded from:

• 1. The mass of the substance

• 2. The temperature change (T)

• 3. The specific heat of the substance (cal or J)

3 Conditions for a Chemical Reaction

1. 1. Collision: Reactions MUST collide

2. 2. Orientation: Reactions must align properly to break and form bonds

3. 3. Energy: The collision must provide the energy of activation

Activation Energy

The amount of energy acquired to break the bonds between atoms of reactants

• 1. If activation energy → Collision energy, the molecules bounce apart without reacting

Exothermic Reaction (Released Energy, -H)

• - Heat is being produced and released into the environment/system!

Endothermic Reaction (Absorbed, +H)

• - Heat is being put into the system/environment

System

The substance(s) undergoing the chemical or physical change

• - EX: Beaker and solution

• → Positive heat is when heat is flowing INTO the system

• → Negative heat is when heat flows OUT of the system

Surroundings

All other matter—including components of the measurement apparatus—but serve to provide or absorb heat from the system.

Work

The process of causing matter to more against on opposing forces

• - At a constant pressure: -work (w) = Pressure (P) x Delta-V (change in volume)

• → -w occurs if done by the system

• → +w occurs if done on the system