Chem Test #3

chemical reaction

the transformation of one or more substances into different substances

gas evolution reactions

reactions that occur in liquids and form gases

combustion reactions

a substance reacts with oxygen, emitting heat and forming one or more oxygen-containing compounds

precipitation reactions

reactions that form solid substances in water

evidence of a chemical reaction

color changes, formation of a solid, formation of a gas, emission of light, emission or absorption of heat

chemical equations

represent chemical reactions

reactants

substances on the left side of the equation

products

substances on the right side of the equation

parentheses next to the formula

we specify the state of each reactant or product in ?

balanced equation

equation in which the numbers of each type of atom on both sides of the equation are equal

how to balance an equation

we insert coefficients in front of the chemical formulas as needed to make the number of each type of atom in the reactants equal to the number of each type of atom in the products

inserting coefficients

changes the number of molecules in the equation, but it does not change the kinds of molecules

determining the # of a particular type of atom within a chemical formula

multiply the subscript for the atom by the coefficient for the chemical formula

aqueous solution

a homogeneous mixture of a substance with water

strong electrolyte solutions

substances that completely dissociate into ions in solution are strong electrolytes and the resultant solutions are

soluble

a compound that dissolves in a liquid

insoluble

a compound that does not dissolve in the liquid

precipitation reaction

a reaction that forms a solid, called a precipitate, when two aqueous solutions are mixed

precipitates

only insoluble compounds form ?

molecular equation

an equation showing the complete neutral formulas for every compound in the reaction

complete ionic equations

equations which show the reactants and products as they are actually present in the solution

spectator ions

some of the ions in solution appear unchanged on both sides of the equation; they do not participate in the reaction

simplify the equation

spectator ions can be omitted to ?

net ionic equations

equations which only show the species that actually participate in the reaction

acid-base equations

reactions that form water upon mixing of an acid and a base

gas evolution reactions

reactions involving a gas; form a gaseous product when the cation of one reactant reacts with the anion of the other

acid characteristics

sour taste, ability to dissolve some metals, tendency to form H+ ions in solution

base characteristics

bitter taste, slippery feel, tendency to form OH- ions in solution

acid-base reactions (neutralization reactions)

generally form water and an ionic compound called a salt that usually remains dissolved in the solution

oxidation-reduction reactions/redox reactions

reactions involving the transfer of electrons

redox reactions

responsible for the rusting of iron, the bleaching of hair, and the production of electricity in batteries; do not always have to involve oxygen

oxidation

loss of electrons

reduction

gain of electrons

combustion reactions (type of redox)

characterized by the reaction of a substance with O₂ to form one or more oxygen-contains compounds, often including water; these reactions are exothermic (emit heat)

synthesis/combination reaction

simple substances combine to form more complex substances; simpler substances may be elements or compounds

decomposition reactions

a complex substance decomposes to form simpler substances; simpler substances may be elements or compounds

decomposition reaction characteristics

require energy in the form of heat, electrical current or light; a number of these reactions require UV light carries more energy than visible light and can therefore initiate the decomposition of many compounds

displacement (single-displacement) reactions

one element displaces another in a compound

double-displacement reactions

two elements/groups of elements in two different compounds exchange places to form two new compounds

Bohr Model & Quantum-Mechanical Model

propose explanations for the periodic law; these models explain how electrons exist in atoms and how these electrons affect the chemical and physical properties of elements

electromagnetic radiation (eg. light)

type of energy that travels through space at a constant speed of 3.0 × 10⁸ m/s (186,000m/s)

wavelength

distance between adjacent wave crests

red light

longest wavelength of visible light with 750nm

violet light

shortest wavelength with 400nm

frequency

the number of cycles or crests that pass through a stationary point in one second

photon

a particle of light existing as a single packet of light energy; the amount of energy carried in the packet depends not he wavelength of the light=the shorter the wavelength, the greater the energy

electromagnetic spectrum

entire range of electromagnetic radiation

gamma rays

the shortest wavelength and more energetic photons; produced by the sun, stars and by certain unstable atomic nuclei on earth; excessive exposure and damage biological molecules

x-rays