Chemistry and Physics: Endothermic, Quantum, and Spectral Concepts

Is the melting of ice endothermic or exothermic?

Endothermic, as heat goes from the surroundings into the ice cube to melt it.

Is the equation H2O → 1/2 O2 + H2 endothermic or exothermic?

since it requires heat to breakdown water, it's endothermic

How much heat is require to raise temp of 7.35g H2o from 21.0C → 98.0C?

2370J

Calculate the specific heat capacity of metal.

- 150g metal heated to 100 degrees celcius

- 50g water, 22C & 28.8C

1. Do Q for water first

2. Q lead = -Q water

3. Solve for C

Specific heat capacity of metal is -0.133J/gC

If a 182g sample of Au is added to 22.1g H2O, the initial water temp is 25C, and the final is 27,5C, and the CAu is 0.128J/gc, what's the initial temperature of Au?

1. negative Qwater + QAu = 0

2. Do Q equation for each & solve for Ti

Initial temp is 37.4

125mL of 0.250M CsOH was mixed with 50mL of 0.625M HF. the temperature went from 21.5C → 24.4C. assume density of all solutions is 1.00g/mL, and the specific heat capacity is 4.2J/gC.

Calculate the change in heat per mol CsOH

-67 KJ/mol

CaO + 3C → CaC2 + CO, ΔH = 464.8 KJ/mol

If 10g CaO reacts with excess C, how much heat is absorbed?

82.9KJ absorbed when 10g CaO reacts

1/2 N2 + O2 → NO2, what is ΔH if the mini reactions are:

a. 1/2N2 + 1/2O2 → NO | ΔH = 90.25 KJ/mol

b. NO + 1/2O2 → NO2 | ΔH = -57.07 KJ/mol

ΔH = 33.18 KJ mol

3C + 4H2 → C3H8, what is ΔH if mini reactions:

a. C3H8 + 5O2 → 3CO2 + 4H2O | ΔH = -2219.1 KJ/Mol

b. C + O2 → CO2 | ΔH = -393.5 KJ/mol

c. H2 + 1/2O2 → H2O | ΔH = -285.8 KJ/mol

ΔH = -104.5 KJ/mol

which would have higher frequency, gamma rays or microwaves?

gamma rays because gamma rays have more energy, so the frequency is higher

which has a higher wavelength? gamma rays of microwaves?

microwaves, because lower energy = higher wavelength

which color of light has the higest energy, blue or yellow?

ROYGBIV, closer to V = more energy

blue would have highest energy

electro magnetic specrum formla

speed of light (3 10&8 m/s) = wavelength frequency

energy = plancks contsant * frequency

calculate the wavelength of light emitted from the n = 4 to n = 2 energy state

486 nm

exothermic

heat from system -> surroundings

endothermic

heat from surroundings -> system

1 calorie

4.184 joules

ΔH°f

forming 1 mole from standard state, measured in KJ/mol

standard state

most common

ie. H -> H2 gas

N -> N2

electromagnetic spectrum formula, poroportionality

c=λ*v

since c = constant, wavelength & frequency are inversely proportoinal

v = frequency

λ = wavelength

photoelectric effect energy formula

photons collide w electrons, electrons increase

E = plancks * frequency

directly proportional to eachother bc E has no limit

how do waves interact with atoms?

light shines on atoms

white light -> prism -> continous spectrum

or white light -> atom -> line spectrum

balmer series

starts at n = 2, for hydrogen atoms

visible spectrum

ROYGBIV

R = Long wavelength, short frequency

V = short wavelength, high frequency

energy level diagram

PUT PHOTO HERE

which e transition has the longest wavelength?

n = 4 -> n = 3

n = 2 -> n = 1

n = 4 -> n=3 would have the longest wavelength because ΔE is smallest, so small frequency, big wavelength

where is the electron?

- in energy level (n-shell -> ℓ-subshell -> mℓ-orbital)

- in orbital (mℓ)

- for hydrogen atom bc hydrogen has only 1 electron, and if there was multiple electrons they would repel eachother

heisenburg uncertainty principle

can't measure position/momentum/energy @ same time

schrodinger

- treated eletrons as wavelength

- wave equations predicted probaility of finding electron in orbital

schrodingers variables

1. n

2. ℓ

3. mℓ

n

- principle quantum #

- possible values: n = 1,2,3...

- show energy lvl/shell

- ctrls size of orbital (distance of electron away from nucleus)

ℓ

- angular momentum #

- possible values: 0,1,2,3 (n - 1 is max)

- shows subshell/grp of orbitals

ℓ subshells

0 -> s

1 -> p

2 -> d

3 -> f

4 -> g

mℓ

- magnetic quantum #

- poss values: mℓ = 0, ±1, ±2, ±ℓ

- each mℓ value -> unique orbital w/ subshell

ie. if ℓ = 2, mℓ can be -2, -1, 0, +1, +2

angular nodes, how to calculate orbitals?

if ℓ = 1, there is a p-subshell of p-orbitals

ie. ℓ = 2, d = 5 orbitals, bc mℓ is -2, -1, 0, +1, +2, (5 values)

if the electron is in n=3, what subshell could it be in?

ℓ = 0 (s), 1 (p), 2 (d) subshell orbitals

# orbitals total

n²

is n = 3, ℓ = 0, mℓ = -1 a possible set of quantum numbers?

no, because since ℓ = 0, mℓ can only be +ℓ (like 1)