CHEM 1311 Midterm 3

ideal gas law formula

PV=nRT

change in energy formula

ΔE=q+w

When heat is absorbed, it is called?

endothermic

When heat is released, it’s called?

exothermic

work (w) is positive (+) when..?

work is done ON the system

work (w) is negative (-) when..?

when the SYSTEM does work

Endothermic

ΔE>0 (energy gain)

q is positive (+)

Exothermic

ΔE<0 (energy loss)

q is negative (-)

Calorimetry is?

measuring heat

Heat capacity (C)

C = q/Δt

Specific heat capaity (c or s)

q needed to raise T by 1 degree Celsius

c = q/mΔt

Specific heat capacity for H2O

4.184 J/C*g

heat energy formula

q=mcΔT

heat energy for a calorimeter

mcΔT = C_calΔT + mC_H2O ΔT

Charles’s Law

V₁/T₁ = V₂/T₂

V is directly proportional to T

_{As gas temperature increases, gas volume increases}

Boyle’s Law

P₁V₁ = P₂V₂

_{P is inversely proportional to V}

_{As gas pressure increases, gas volume decreases}

Avogadro’s Law

V₁/n₁ = V₂/n₂

_{V is directly proportional to n}

_{As the number of moles of gas increases, gas volume increases}

Combined Law

(P₁V₁)/T₁ = (P₂V₂)/T₂

_{V is directly proportional to T/P}

Moles formula

mass/molar mass

1 atm equals?

760 torr

760 mm Hg

101.3 kPa

14.7 psi

Dalton’s Law of Partial Pressure: For a mixture of gases in a container…,

P_total = P₁ + P₂ +P₃ +…

density formula

d = ((MW)P) / (RT)

root mean square velocity of gases (rms)

u_rms = rt(3RT/M) in m/s

Graham’s Law

The rate of effusion and diffusion of a gas are inversely proportional to the square root of its molar mass.

Lighter gas molecules move faster and effuse/diffuse quicker than heavier molecules. The law applies to gases at constant temperature and pressure

As mass increases, speed decreases

kinetic molecular theory

If temp ↑, then kinetic energy ↑, and rate of collisions ↑ and vice versa

KMT: If volume is decreased..?

everything is the same, but collisions ↑ (V decreased)

KMT: If temp is increased…?

Kinetic energy ↑, velocity ↑, collisions ↑

KMT: If number of moles increase…?

everything is the same but collisions ↑

Kinetic energy formula

KE = 1/2mv²

Gases behave ideally at?

High temps and low pressures

What is the standard temperature and pressure (STP)?

temp: 273 K

pressure: 1 atm

volume: 22.4L

what are intermolecular forces?

forces between MOLECULES

London dispersion forces (LDF)

• anything with electrons

• nonpolar molecules will ONLY have LDFs

• anything with just C and H is nonpolar

Dipole-dipole

• polar covalent bond

• POLAR

hydrogen bonding

H bonded with N, O, F

ion-dipole

ionic bonds

strength of IMFs from weakest to strongest

LDF < dipole-dipole < hydrogen bonding < ion-dipole

Stronger IMFs mean?

• higher melting/boiling point

• heavier/bigger elements and molecules

• higher viscosity

• lower vapor pressure

Larger molecules mean?

• Higher: surface tension, viscosity, boiling point

• stronger IMFs

• more molecular mass → attractive forces stronger

• enthalpy of vaporization is greater for bigger molecules

A less polar molecule would have a…?

lower viscosity

If a molecule is nonpolar, it will have…?

a lower surface tension

work formula

w = -PΔV

Enthalpy formula

ΔH = ΔE + w

ΔH_rxn

ΔH_rxn = ΔH_products - ΔH_reactants

ΔH =

ΔH = [(energy of bonds broken) - (energy of bonds formed)]

What is Hess’s Law?

ΔH = ΔH₁+ΔH₂+ΔH₃+…

q_calorimeter

=C_calorimeterΔT

mole fraction formula using pressure

X₁ = P₁/P_Total

mole fraction formula using moles

X₁ = n₁/n_Total

KE_avg

3/2 RT

What is the triple point on a phase change diagram?

the temp and pressure where all three phases are in equilibrium

What is the critical point?

The point at the end of the liquid-gas boundary, beyond this point substances become supercritical fluids

solid → gas

sublimation

gas → solid

deposition

solid → liquid

melting (fusion)

liquid → solid

freezing

liquid → gas

vaporization

gas → liquid

condensation