Chemical and Physical Changes: Reactions and Laws
Physical Changes
Physical changes occur when some properties change, but the substances remain the same.
Chemical Changes
Chemical changes occur when some substances are transformed into others. There is an exchange of energy.
Causes of Chemical Bonds
The causes of chemical bonds are electromagnetic forces.
Chemical Reaction
A chemical reaction is the process by which chemical changes occur.
Chemical Links
Interactions are produced by electrons:
- Ionic Bond: Metal + Non-metal. The non-metal loses electrons, forming two ions of opposite charge.
- Covalent Bond: Non-metal + Non-metal. They share a pair of electrons between the two atoms, acquiring the electrical structure of a noble gas.
- Metallic Bond: Metal + Metal. They lose electrons in the last layer and become positive ions enveloped in a cloud of negative electrons.
Reagents
Reagents are the substances that react in a chemical process.
Reaction Products
Reaction products are the substances formed in a chemical process.
Law of Conservation of Mass
The mass of the reactants equals the mass of the reaction products.
Law of Constant Proportions
When substances combine to form others, they always do so in a constant mass relationship.
Mole
One mole contains 6.022 * 1023 molecules.
Synthesis Reactions
Starting from single atoms, more complex molecules are obtained.
Decomposition Reactions
A complex substance breaks down into simpler ones.
Exothermic Reaction
An exothermic reaction gives off heat.
Endothermic Reaction
An endothermic reaction needs heat to be produced.
Chemical Equation
A chemical equation is the mathematical representation of a reaction.
Ammonia
NH3
Atomic Number (Z), Mass Number (A), and Isotopes
Isotopes: Same Z, different A.
Groups in the Periodic Table
Noble or inert gases, noble metals, alkali metals, non-metals, halogens, and semimetals.
Ion
An ion is an atom that is missing or has an extra electron (cation = positive, anion = negative). Rutherford’s global model.
Percentage Mass
Mass % = [Mass of solute / Mass of solution] * 100
Percentage by Volume
Volume % = [Volume of solute / Volume of solution] * 100
Grams per Liter
Concentration = Mass of solute / Volume of solution
Concentration (Molarity)
Concentration = Amount of solute (in moles) / Volume of solution (in liters)
General Gas Law
Pressure * Volume / Temperature
Unit conversion example: 120km/1h; 1000m/1km; 1h/3600s
Isotopes
Same number of protons (atomic number).
Atom
A pure substance containing a single element.
Molecule
A pure substance containing multiple elements.
Ebullioscopy
The ebullioscopic increase is proportional to the number of solute particles present.
Osmosis
All cells are nourished, and waste is eliminated through membranes. Osmosis involves a semipermeable membrane.
Solubility
Solubility is the maximum amount of a substance that can dissolve in 100g of solvent at a given temperature.
Element
An element cannot be decomposed into simpler substances.
Compound
A compound’s molecules are formed by two or more elements. It can be decomposed or broken down into atoms and is inseparable.
Warming Curve
At 0°C, there is solid and liquid (a change of state occurs here). At 100°C, there is liquid and gas (another change of state occurs). From -50°C to 0°C, it’s solid; from 0°C to 100°C, it’s liquid; and above 100°C, it’s gas.
Pure Substance
Pure substances include elements (ordered in the periodic table and represented by a symbol) and compounds (formed by several atoms).