Equations to Memorize

Question 1

What do these letters stand for, and what are their units?

λ

v

c

E

h

Answer 1

• λ= wavelength: the distance between peaks in a cycling wave (units: meters)
• v=frequency: the number of wave cycles per second (units: Hertz)
• c= speed of light: 3.00x10⁸ m/s
• E= energy (units: Joules)
• h= Planck’s constant: 6.6262x10^-34Js

Question 2

What is the equation for the speed of light?

Answer 2

c = λv

where c= speed of light: 3.00x10⁸ m/s

λ= wavelength (m)

v=frequency (Hertz)

Question 3

What’s the equation for the energy of a photon?

Answer 3

E = hv

E = hc/λ

where h = Planck’s constant: 6.6262x10^-34Js

v= frequency (Hertz)

c = speed of light 3.00x10⁸ m/s

λ= wavelength (m)

Question 4

What’s the equation for wave particle duality?

Answer 4

λ = h/mv

Any moving particle has a wave associated with it. This is the wavelength.

Question 5

How do you calculate energy using specific heat?

Answer 5

q = mc ΔT

Same as q = ncΔT (when you’re given moles) and

q = msΔT (when you’re given specific heat vs. heat capacity)

• If q is positive, the system is gaining energy, endothermic.
• If q is negative, the system is losing energy, exothermic.

Question 6

What is Avogadro’s number?

Constants we will be given:

h (Planck’s constant)

c (the speed of light)

Answer 6

Avogadro’s: 6.02×10²³ units in 1 mole

h = Planck’s constant: 6.62606×10⁻³⁴ J·s

c = Speed of light: 3.00x10⁸ m/s

Question 7

What is Coulomb’s formula?

Answer 7

• Force of attraction or repulsion is directly proportional to the magnitude of the charges, and inversely proportionally to the distance between the particles. So as ion charges increase, the force increases. As distance increases, the force decreases.
• The sign of the charges matter for showing us the direction - attraction or repulsion

Question 8

What is the equation for heat transfer,

and what do the variables stand for?

Answer 8

q = msΔT

can also be written

q = nCΔT

q = heat (energy units, Joules)

m = mass (g)

n = moles

s = specific heat capacity (when working with grams) J/g° C

C = heat capacity (when working with moles) J/moles° C

q_surroundings = -q_system

Question 9

What is the equation for a change in energy?

(The first law of thermodynamics)

Answer 9

ΔE = q + w

a change or transfer of energy = heat + work

In the lab, measure with bomb calorimetry: ΔE = q_volume

In the lab, measure with coffee cup calorimetry: ΔH = q_pressure

(enthalpy is energy without the work, basically the same if no gases produced)

Question 10

What is the equation for work?

Answer 10

w = -PΔV

• Work is movement against a restraining force
  
  • Context: expansion of a gas. Look for creation of gas molecules Δn_gas.
• P pressure is always positive. ΔV is always positive for expansion of a gas, because growing volume
• If “w” work is negative, that means your system has done work. Exothermic.

Question 11

What is the equation for enthalpy of reaction?

(Hess’ Law)

Answer 11

ΔH_rxn = ΔH_products - ΔH_reactants