Exam 2: Chapters 2,6,7

measurement

determines capacity, quantity, or extent of something
- involve both number and associated unit

Mass base unit

gram (g)

Length base unit

meter (m)

volume base unit

liter (L)

1mL = 1cm^3

definition, it is exact (infinite SFs)

Weight is dependent on

gravity (mass is not)

Mass

independent of gravity and is the amount of matter in sample

mega-

M - million

kilo-

k - thousand

deci-

d - tenth, 10^1

centi-

c - hundredth, 10^2

milli-

m - thousandth, 10^3

micro-

μ - millionth, 10^6

exact number

no uncertainty when counting individual items or from definition

inexact number

most measurements and calculations will have uncertainty
not known exactly (have limited amount of SFs)

significant figures

digits in number that are known with certainty + one uncertain digit (last)

taking a reading from instrument with gradations

one digit past the gradations

all nonzero digits are

significant

leading zeros are

not significant

confined zeros (zeros between nonzero) are

significant

trailing zeros (no decimal- 345,000) are

not significant

trailing zeros (decimal - 345.00) are

significant

rounding in multiplication/division

least # of SFs in calculation determines # SFs in result

rounding in addition/subtraction

the number that has the least significant digits to the right of decimal

in correct scientific notation there is only

1 digit to the left of the decimal place (1.2 x 10^3)

Metric to English conversion factors are not exact except for

1 in = 2.54 cm

Dimensional Analysis process

Sort
Strategize
Solve
Check: reality, units, sig figs

density

ratio of mass of object to its volume
physical property that is unique to any substance

reasonable densities

about 0.5g/ml to 20g/ml

celsius scale

based on freezing (0°C) and boiling point of water (100°C), metric

Kelvin

based on absolute zero (0°K) with intervals = to Celsius scale
- Kelvin scale is always positive

absolute zero

lowest temperature possible (0°K), when all molecular motion ceases

Fahrenheit

currently based on freezing (32°F) and boiling point of water (212°F)
- used mainly in US

formula mass

mass in atomic mass units (amu) for an ionic compound or molecule

how to calculate formula mass

using atomic masses of elements in a chemical formula

mole

(n) 6.02x10^23 of something also called Avogadro's number

molar mass (MM)

mass of a mole of something in units of grams (g/mol)

molar masses of elements are listed where

periodic table as their amu

how to calculate molar mass of a compound

same way as formula mass

chemical equation

way to write what happens in a chemical reaction
using formulas for reactants and products
A + B --> C + D

chemical equations are balanced by placing _______ in front of each reactant and product

coefficients

coefficient

applies to every element in a substance unlike formula subscripts that only apply to individual elements
- should be the smallest, whole numbers possible

easiest to start with the

most complex reactant or product with small integer

aqueous (aq)

substances dissolved in water

solid (s)

solids and insoluble ionic compounds

liquid (l)

liquids

gas (g)

gases

stoichiometry

coefficients from the balanced chemical reaction relate the # of reactants used in a chemical reaction and the # of products created

yield

amount of product (typically in grams) produced in a reaction

theoretical yield

the yield predicted based on an amount of reactant and using the reaction stoichiometry

actual yield

amount actually obtained in experiment

percent yield

how much of the theoretical yield was actually produced
(actual yield/theoretical yield) x 100%
- percent yield is often close to 100%
- may be significantly less due to equilibria, side reactions, and experimental procedure

limiting reactant

the reactant that is completely consumed in a reaction AND will limit (and determine) the amount of product that can be formed (the theoretical yield)

excess reactants

reactant that has more than enough compared to the limiting reactant

when there is a limited amount of more than one reactant a calculation must be done to determine

which reactant is the limiting reactant

g ↔ mol

use molar mass (MM)

number ↔ mol

avogadro's number

mol compound ↔ mol element in compound

formula subscripts

compressibility

a measure of the change in volume as pressure is increased

thermal expansion

a measure of change in volume as temperature is increased

Kinetic Molecular Theory of Matter

cohesive forces

(potential energy) between atoms or molecules ("stickiness of molecules" - IMF)

disruptive forces

results from (kinetic energy), as a function of temperature of the substance

when temperature increases, disruptive forces___

increase, separating atoms or molecules and leading to liquid and then gas phases for a substance

KE<PE (low temp)

solid

KE≈PE (medium temp)

liquid

KE>PE (high temp)

gas

solid state:

volume and shape: definite volume and shape
density: high
compressibility: small
thermal expansion: very small

liquid state:

volume and shape: definite volume, indefinite shape (takes shape of the container)
density: high (lower than corresponding solid)
compressibility: small (greater than corresponding solid)
thermal expansion: small

gas state:

volume and shape: indefinite volume and shape
density: low
compressibility: large
thermal expansion: moderate

gas laws:

mathematical relationships between gas pressure, volume, temperature, and the amount (moles) of a gas

pressure

force applied per unit area on an object
pressure of a gas is due to particles colliding with the surface of the object

volume

an amount of a 3D space

temperature

measure of the amount of kinetic energy of molecules
(must be converted from C to K)

Amount

mass of number of gas particles (moles)

Boyle's law

relationship between pressure and volume (gas compressibility), when #moles and temperature don't change
- linear/inverse relationship: 2x pressure --> 1/2 volume
- when one unit increases the other decreases
- any units can be used (but consistent)

Charle's Law

relationship between volume and temperature (gas thermal expansion)
- linear/direct relationship: 2x temp --> 2x volume (as P and T don't change)
- when one unit increases so does the other

Combined Gas Law

relates changing pressure, volume, and temperature (moles stay constant)

Ideal Gas Law

relates all four gas law varibles (P,T,V,n) as long as none of them are changing
- must be in units of R (L, atm, mol, K)

Dalton's Law of Partial Pressure

total pressure exerted by a mixture of gases is the sum of the partial pressures of individual gases present

State change

when substance changes from one phase (solid, liquid, or gas) to another

endothermic

occurring as the substance is being heated (heat is absorbed) - more kinetic energy

What phases are endothermic

1. melting (solid to liquid)
2. evaporation (liquid to gas)
3. sublimation (solid to gas)

exothermic

occurring as substance is cooled (heat is released) - less kinetic energy

What phases are exothermic

1. condensation (gas to liquid)
2. freezing (liquid to solid)
3. deposition (gas to solid)

Evaporation

process where molecules escape from liquid phase to gas phase

evaporation occurs at the___of a liquid

surface
- molecules escape the liquid if they are moving in 1. correct direction and 2. have sufficient energy

As temperature increases___molecules at the surface have sufficient energy to escape, and evaporation occurs at a faster rate

more

Due to evaporation, most liquids in closed container will have some particles of substance in gas phase, above liquid

what is the gas above a liquid called?

vapor

as a substance evaporates in a closed container, the vapor pressure slowly _____ until the_____ is reached and ____ will no longer change

1. increase
2. equilibrium vapor pressure
3. pressure

vapor pressure

pressure exerted by a vapor above a liquid when the liquid and vapor are in physical equilibrium with each other

vapor pressure depends on

nature and temperature of substance

nature of substance

substance that has strong IMF will have low vapor pressure and conversely a substance that has weak IMF will have a high vapor pressure

volatile substance

substance that readily evaporates at room temperature- -high vapor pressure (weak IMF)

temperature of liquid in vapor pressure

as temperature increases, molecules gain more kinetic energy, and evaporate more often --leads to higher vapor pressure

boiling

special case of evaporation, occurs at the unique temperature where VP=external pressure (atm)
- liquids can create bubbles (go from liquid to gas) WITHIN the liquid

boiling point

where vapor pressure = atmospheric pressure

temperature a substance boils will change with

external pressure

normal boiling point

is the temperature that a substance boils at under 1 atm of pressure