Chemistry Equations

Question 1

What is the equation for heat transfer (no phase change)?

Answer 1

q= heat
m= mass
c= specific heat of the substance
∆T= (T _initial- T _final)
L= latent heat (cal/g)

Question 2

What is the equation for heat transfer with phase change?

Answer 2

q=mL

q= heat
m= mass
L= latent heat (cal/g)

Question 3

What is the equation for entropy?

Entropy is the degree to which energy has been spread throughout a system or in-between systems.

Answer 3

∆S= Change in Entropy, units= J/(mol*K) (When energy goes into a system, entropy INCREASES. When energy goes out of a system, the energy decreases)
Q_rev= heat that is gained or lost in a reversible process
T= temperature in Kelvin

Question 4

What is the equation to evaluate gibbs free energy?

Answer 4

∆G= ∆H - T ∆S

∆G= Gibbs free energy
∆H= enthalpy
T= temperature
∆S= Entropy
Mnemonic= Goldfish are horrible without tarter Sause

Question 5

What is the equation to get standard Gibbs free energy from the equilibrium constant?

Answer 5

∆G°_rxn=-RT ln K

If K is less than 1, lnK will be negative
If K is greater than 1, lnK will be positive.

∆G°_rxn = standard free energy
R= the ideal gas constant
T= temperature in kelvin
K_eq= equilibrium constant

Question 6

What is the equation to get Gibbs free energy from the reaction quotient?

Answer 6

∆G°_rxn = standard free energy
R= the ideal gas constant
T= temperature in kelvin
K_eq= equilibrium constant
Q= reaction quotient.

Question 7

What is the equation for the enthalpy of bond dissociation?

Answer 7

CHANGE THIS ONE

ΔH°_rxn = Σ Δ_{Hbonds broken} − Σ Δ_{Hbonds formed}

Question 8

What is the specific heat of water? Liquid?

Answer 8

1 (cal)/(gram x Kelvin)

or

4.186 J (g K)

Question 9

How do you calculate the Equilibrium constant? K_eq

Answer 9

[C,D,A,B] are the given concentrations, moles/L, while c,d,a,b (exponents) are the moles

***This is NOT the rate of the reaction, where we need to find the rate empirically. Instead, we can find equilibrium by this formula using the moles to guide us.

Question 10

What is the rate law equation?

Answer 10

rate law = k [A]^x[B]^y

x & y are NOT a and b.
They must be determined empirically.
So they will give you an example of concentrations, and then changes in the product, and you will determine x and y from that
x= 0 (no change in concentration), x=1 (product doubles if concentration doubles), x=2( if reactant increases by 2, the product quadruples)

Question 11

What is the equation of the first law of thermodynamics?

Answer 11

∆U= Q – W

∆U = change in the internal energy of the system
Q= heat added to the system
W= work done

Question 12

What is the equation for the enthalpy of bond dissociation?

enthalpy = heat

Answer 12

ΔH°_rxnrxn = Σ ΔH_products − Σ ΔH _reactants

ΔH°_rxnrxn = Σ ΔH_{bonds broken} − Σ ΔH _{bonds formed}

Question 13

How is EMF (E°_cell) calculated?

Answer 13

The EMF is calculated by
EMF (E°_cell)= E°_{red cathode} - E°_{red anode}

If EMF/E°_cell is +, it is spontaneous
If EMF/E°_cell is -, it is not spontaneous (electrolytic cell)

Question 14

What is the standard electromotive force (EMF), and how does this relate to the Standard reduction potential?

This assumes standard conditions (298 K, 1 atm, and 1M concentrations)

What is the equation?

Answer 14

Standard EMF (E°cell) is the difference between the reduction potential of two half reactions in the battery.

If the difference is Positive, it will occur spontaneously (galvanic).

If the difference is negative, it will not be spontaneous and require energy (electrolytic)

Question 15

What is the equation that describes the relationship between ∆G° and EMF (electromotor force) ?

Assuming standard conditions.

Answer 15

∆G°= -nFE°cell

∆G°= standard change in free energy
n= number of moles of electrons
F= faraday constant= 1F= 96,485 C
E°_cell= EMF of the cell

Important= if Faraday Constant is expressed in coulombs, then ∆G must be expressed in J, not kJ

Question 16

What is the Nernst equation, and what is it used for?

Answer 16

describes the relationship between the concentration of species in a solution under non-standard conditions and the electromotive force.

NON-STANDARD conditions is the key here.

E_cell=EMF under nonstandard conditions
E°_cell= emf of the cell under standard conditions
R= ideal gas constant
T= temperature, in Kelvin
n= number of moles
F= farady constant= 1F= 96,485 C
Q= reaction quotient for the reaction at a given point in time (remember, don’t include solids or pure liquids

Question 17

Graham’s Law describes the behavior of gas diffusion or effusion, stating that gases with lower molar masses will diffuse or effuse faster than gases with higher molar masses at the same temperature.

What is the equation?

Answer 17

r1 and r2 are the diffusion rates of gas 1 and 2

M1 and M2 are the molar masses of gas 1 and gas 2

Question 18

What is the equation to calculate the speed of a gas particle?

Answer 18

U= speed
R= ideal gas constant= 8.314 (J)/(mol x K)
T= temperature (K)
M= molar mass

Question 19

What is the equation for percent composition by mass?

Answer 19

Question 20

How is molarity calculated?

Answer 20

Molarity (M)= moles of solute/ liters of solution

Question 21

If you wanted to find the concentration of a solution after diluting one, what equation would you use?

Answer 21

M_iV_i= M_fV_f

Question 22

What is the equation for vapor pressure depression? or Raoult’s Law?

Answer 22

The presence of other solutes decreases the evaporation rate of a solvent without affecting its condensation rate, thus decreasing its vapor pressure

P_a=X_aP_a°

P_a= the vapor pressure of solvent A when the solutes are present
X_a = is the mole fraction of the solvent A in the solution (moles solvent/total moles (solvent + solute)
P_a°= the vapor pressure of solvent A in its pure state.

The presence of the solute molecules can block the evaporation of solvent molecules but not their condensation.

Question 23

What’s the equation for boiling point elevation when there’s a solute added to the solvent?

Answer 23

∆T_b= iK_bm

∆T_b= increase in boiling point

i= van’t Hoff Factor =corresponds to the number of particles into which a compound dissociates in a solution, for example, NaCl= 2, because NaCl dissolves into Na and Cl. Molecules like sugar do not dissociate so have a value of 1

K_b= proportionality constant of a particular solvent

m=molarity of solution

Question 24

What is the equation for freezing point depression?

Answer 24

∆T_f= iK_fm

∆T_f= increase in freezing point

i=van’t Hoff Factor =corresponds to the number of particles into which a compound dissociates in a solution, for example, NaCl= 2, because NaCl dissolves into Na and Cl. Molecules like sugar do not dissociate so have a value of 1

K_f= proportionality constant of a particular solvent

m=molarity of solution

Question 25

What is the Faraday’s constant equation? I.e. tells you how many moles of something will be produced using electricity?

Answer 25

Question 26

What is the mathematical relationship between K_a, K_b, and KK_w?

Answer 26

K_a x K_b = K_w

K_w= water constant= 7

Question 27

What is the Henderson-Hasselbalch Equation and what it is its purpose?

Answer 27

It us used to estimate the pH or pOH of a buffer solution

[A-]= concentration of the conjugate base
[HA]= concentration of the weak acid

Question 28

How do you figure out the pH when you have a decimal with number?

i.e. What is the pH of a solution with a concentration of hydrogen atoms of 3 x 10^-4?

Answer 28

pH=m-log(n)

pH= n x 10^m

p[OH or H]= m-0.n

pH= 4-0.3= 3.7

Question 29

What is the equation to get ∆G from the K_eq?

Answer 29

∆G=-RTlnK_eq

If K_eq is < 1, lnK will be positive, making ∆G negative.

If K_eq is > 1, lnK will be negative, making ∆G negative (note the double negative).