General Chemistry for Engineers Midterm 1

chemistry

the study of structure, composition, & properties of matter; energy flow during physical and chemical change

matter

an entity which has mass and occupies space (has volume)

mass

measures amount of matter in grams

analytical balance

utilized to determine mass (in grams) in laboratory setting

weight

measures the earth's gravitational force on an object (measurement of force)

W=mg

g = gravitational acceleration (9.8 m/s^2)

units: pounds (Lbs)

force

an action that causes acceleration or deformation of an object (a push or pull)

Newton's Second Law of Motion

acceleration of an object depends on the mass of the object and the amount of force applied (F=ma);

measured in Newtons (N) which is kg m/s^2

weight is _____________ to mass

proportional

volume

amount of space occupied by matter

typical units: mL, cm^3, or L

displacement

used to determine volume of irregular objects

1.) Fill a graduated cylinder and record volume

2.) Add object to water

3.) Calculate: Vobject=Vfinal-Vinitial

density

amount of matter per unit volume (concentration)

d=m/v

typical units: g/mL, g/cm3, or, for gases, g/L

solids, liquids, and gases ____________ upon heating and ___________________ upon cooling

expand, contract

Temperature affects _____________ in d=m/v. Thus, __________________ ____ _____________ varies with temperature

volume (v), density of matter

Matter is dichotomized into 2 categories being....

purse substances and mixtures

pure substance

material of fixed composition

1.) elements

2.) compounds

elements

pure substances comprised of one type of atom

# of protons

atomic number

# of neutrons

atomic mass - atomic number

# of electrons

# of protons (+ or - any charges)

atom

smallest particle unit of an element (retains properties of element)

groups

vertical columns

periods

horizontal rows

compounds

pure substances comprised of two or more elements chemically combined in a fixed ratio as a result of chemical reactions between elements

molecule

independent structural unit comprised of two or more atoms that are chemically bound together

molecules can be

diatomic, triatomic, and polyatomic

mixtures

-one or more different substances

-substances that are physically intermingled

-variable composition

-can be homogenous and heterogeneous

homogenous mixtures

-appear as a single, uniform phase

-constituents are not distinguishable

ex: mouthwash, saline rinse

heterogenous mixtures

-appear as a multi-component entity

-boundaries between constitutes visible

ex: sandwich, muddy water

physical change

-phase or state of matter changes

-chemical composition remains constant.

physical change is initiated by...

changes in temperature and pressure

fusion

solid to liquid (melting)

freezing

liquid to solid

vaporization

liquid to gas

condensation

gas to liquid

sublimation

solid to gas

deposition

gas to solid

mixture

-contains two or more components

-components are physically intermingled

-can vary in its composition

physical properties

characteristics of a material when it is not undergoing change

-metals are shiny, malleable, electrically conductive

-ammonia gas has a strong odor

-aluminum oxide is a brittle solid

-chlorine is a pale-green gas

chemical properties

refer to behaviors of matter while undergoing chemical change

-octane is flammable

-iron rusts in the presence of moisture

-copper rooftops turn green over time

-sodium explodes when added to water

4 observations consistent w/ chemical change

1.) temperature change

2.) color change

3.) evolution of a gas

4.) formation of an insoluble solid

temperature

measures

-how hot or cold a substance is

-average particle energy of motion (kinetic energy)

typical units: Celsius and Kelvin

celsius to kelvin conversion formula

Tk = Tc + 273.15

exothermic reaction

-temperature increases

-heat flows from system into surroundings

-system feels warm to touch

endothermic reaction

-temperature decreases

-heat flows from surroundings into system

-system feels cold to touch

color change

indicates system interacts differently with ambient light

evolution of a gas

appearance of bubbles, as a result of combining 2 unalike substances

precipitate formation

in a precipitation reaction, when 2 clear liquids are combined and insoluble solid appears

Law of Conservation of Mass

-matter is conserved in a chemical reaction

-matter is neither created nor destroyed.

Law of Definite Composition

regardless of origin, a compound contains the same elements in the same ratios by mass

% mass of element

% mass of element = (mass element/mass compound) * 100

mass average equation

m ave = (mass 1 amu 1) + (mass 2 amu2)

Law of Multiple Proportions

If two masses of an element react with a defined mass of a second element to form two different compounds... The two masses of the first element form a ratio of small-whole numbers

energy

the ability to do work

work

force applied to an object over a given distance

W=Fd

typical units: m^2/s^2, Newton-meter (N*m), Joule

4 forms of energy

thermal, luminous, electrical, nuclear

Rules for significant figures

- all non zero digits are significant

- zeros between nonzero digits are significant

- zeros preceding nonzero digits are not significant figures

- zeros at the end of a number with a decimal place present anywhere are significant

- zeros at the end of a number with no decimal present are not significant

how many sig figs are in 100?

1 sig fig

how many sig figs are in 0.0410?

3 sig figs

how many sig figs are in 0.0011?

2 sig figs

addition & subtraction w/ significant figures

Watch decimal places!

A sum or a difference is reported to the same number of decimal places as the measurement in the calculation with the fewest decimal places.

Example: Volume = 83.5 mL + 23.28 mL + 106.8001 mL Volume = 213.6 mL

multiplication & division w/ significant figures

Watch total sig figs in each measurement

The product or quotient is reported using the same total number of sig figs as the value entered into the calculation with the fewest

Example: Volume = (9.2 cm)(6.81 cm)(0.3744 cm) Volume = 23 cm3

logarithms w/ significant figures

a calculated log value should contain the same number of decimal places to the decimal as there are significant figures in the value used

Example: log10(3.67x 10-3) = -2.435

accuracy

how close a measurement is to an accepted value

percent error

used to assess how far a measured value is from an accepted value

percent error formula

% error = (measured value - accepted value) / (accepted value) * 100

precision

refers to how close a collection of measured values are with respect to one another

Example: Three different students record the following measurement for a liquid in a graduated cylinder

-32.2 mL

-32. mL

-32.3 mL

Note how close these values are to one another

There is high precision among these measurements

giga-

G 10^9

mega-

M 10^6

kilo-

k 10^3

deci-

d 10^-1

cenit-

c 10^-2

milli-

m 10^-3

micro-

μ 10^-6

nano-

n 10^-9

pico-

p 10^-12

femto-

f 10^-15

International System of Units (SI Units)

MKS provided foundation for this system

Meter (length)

Kilogram (mass)

Second (time)

Ampere (current)

Kelvin (Temperature)

Mole (amount)

Evidence that light behaves as a wave

reflection, dispersion, refraction, diffraction

specular reflection

arises from illuminating polished surface (ex: mirror)

diffuse reflection

arises from illuminating rougher surfaces

dispersion

shining white light through prism separates light into different wavelengths so we see a rainbow

refraction

light changes velocities when traveling in air vs. water (objects in water appear to bend)

diffraction

when light strikes edge of object, it bends around it

Young's double slit experiment

shows the constructive and destructive interference of waves that occur as light passes through parallel slits, resulting in dark spots from out-of-phase waves destructively interfering (nodes) and light spots from in-phase waves constructively interfering

electromagnetic radiation

a form of energy that exhibits wavelike behavior as it travels through space

electromagnetic spectrum trends

long wavelength = low frequency & low energy (radio waves)

short wavelength = high frequency & high energy (gamma rays)

wavelength

(lambduh) horizontal distance between the crests or troughs of two adjacent waves

amplitude

height of wave (determines intensity/brightness)

frequency

(v = "nu") # of cycles per second / how often signal is detected per unit of time

frequency and wavelength relationship

inversely related (lower frequency = higher wavelength)

c= lambduh * frequency

the quantum concept: blackbody radiation

coals in campfire glow red and finish at blue/white, proceeding from long to short wavelength on EM spectrum

quanta

discrete packets of energy (exchange between matter and energy occurs in quanta)

energy and frequency relationship

directly proportional

E=nhv

n = # of photons

v = frequency

h = Planck's constant

Bohr model of the atom

-electrons move in circular orbits about the nucleus

-electronic motion described by classical physics (planets around sun)

-electron has fixed set of orbits called stationary states

-as long as the electron remains in a given orbit, its energy is constant

-energy is neither emitted nor absorbed if electron remains in orbit

-an electron can pass only from one allowed orbit to another

-electron transitions result in light absorption and emission

-this light is rendered as discrete bundles of energy, called quanta

-caused shift to quantum mechanics

problems w/ the Bohr Model

-Bohr Model is obsolete in 21st century

-inability to explain multi-electron systems

-no explanation for magnetic field effects on atomic-emission spectra

-no basis for quantized angular momentum forcing electrons in orbits

-electron expected to spiral into nucleus due to attraction between positive nucleus & negative electrons

quantum theory

a model of matter and energy based on the principle that energy is absorbed or emitted in discrete packets (quanta)

quantized

-having values restricted to whole-number multiples of a specific base value (n is quantized)

-Planck proposed that objects emit EMR in integral numbers of quantum defined by E = hv

equation that relates energy of a quantum of electromagnetic radiation to its wavelength

E = hc / lambduh

emission

release of light from excited state atoms (when electrons return to lower n, energy is released)

absorption

promotes electron to higher energy (excited state)