Download Dr. Maleckar Review Sheet Pitt Exam #2

Maleckar
CHS Chemistry
2016-2017
Chapter 4 Leftovers:
- be able to calculate limiting reagents/theoretical yield/% yield
Exam 2 Review Sheet
- be able to use molarity in stoichiometry problems
- be able to calculate the overall % yield of a multi-step reaction
EX)If you have a series of reactions……
A→B→C→D
And the first step (A → B) is 92% yield, and the second step (B → C) is 76% yield, and the third step (C → D) is 85% yield, what
is the overall % yield for the three steps? Just multiply the % yields of the individual steps together.
(0.92)(0.76)(0.85) = 0.59432 = 59% yield
Chapter 5: Gases
- Empirical Gas Laws
Boyle’s Law (T const) P,V indirectly proportional
Charles’s Law (P const, piston movable lid) V,T directly proportional
Avogadro’s Law (P,T const) V,n directly proportional
Guy-Lussac (V const, rigid container) P,T directly proportional
Combined Gas Law
Ideal Gas Law (applies to one gas PgasV = ngas RT) (applies to a mixture of gases, PtotV = ntot RT) R = 0.0821
- understand how a gas is different from solids and liquids on a molecular level
- be able to use the Ideal Gas Law in the context of stoichiometry and a balanced reaction to determine quantity of a gas needed or
produced, etc PV = nRT
- be able to calculate the density of a gas (units: g/L) “DUMP RAT” D = (MP)/(RT)
- be able to perform calculations involving mixtures of gases (the individual pressures of the gases add up to the overall pressure)
Dalton’s Law of Partial Pressures P tot = P1 + P2 + …. gas is collected over water Ptot = Pdry gas + PH2O
Mole Fraction =
or =
and therefore
=
- know and understand kinetic molecular theory – (Pg199-200 in book, memorize!)
increase/decrease the temp and how and why that changes the kinetic energy of the gas particles, its speed, the force with
which it collides with the vessel walls, and the pressure within the vessel
- the speed of gas molecules increases as T goes up, and decreases as MW goes up (root mean square speed, rms)
- be able to calculate the root mean square speed rms of a gas molecule (watch your units) rms = √
where R = 8.31
- be able to use/manipulate Graham’s Law for effusion/diffusion problems
- be able to use the van der Waal’s equation, if given a and b for a gas
- understand under what conditions a gas behaves non-ideally (low temp and high pressure)
- be able to use the gas laws with stoichiometry, theoretical yield, etc.
Chapter 6: Thermodynamics
- Total Internal Energy of the System ΔE = q+w Takes the system’s perspective
- w= -PΔV work is dependent on the change in volume of the system
- “We are chem we are jive 101.325 Joules” conversion from L atm to Joules
- Be able to tell when q is positive or negative; be able to tell when w is positive or negative
- First Law of Thermodynamics: energy is conserved or energy is neither created nor destroyed, but it can be transformed or there
is no free lunch! Heat gained = - Heat lost
- enthalpy (H) is a measure of the energy (heat) absorbed or generated by a reaction at constant pressure
- we can’t easily know that absolute enthalpy in a system, but it is easy to measure ΔH,if ΔH(+), endothermic; if ΔH(-), exothermic
- be able to calculate ΔH by these methods:
- using the enthalpies given ΔHrxn = ΣnΔHproducts - ΣnΔHreactants
- using Hess’s Law (manipulate the reactions – puzzle method)
- be able to scale enthalpy up or down depending on the stoichiometry in a reaction (Stoichiometry of the reaction based on the
definition of Thermochemical Equation) Ex: if the ΔH for the combustion of a hydrocarbon is -400 kJ/mole, how many kJ are
released when 50g of that hydrocarbon are combusted?
- be able to use specific heat to calculate the energy needed to heat/cool substances, especially water……also be able to do
calculations involving the phase changes of water
- be able to do bomb calorimeter and coffee cup calorimeter problems q (energy) = mSΔT or q = mCΔT depending on units! Same
calculation s units are J/gºC and C units are J/gK
- Heat Energy of a Calorimeter q = CΔt where C= units of J/ºC or J/K
- s=4.18 J/gºC for water (a high value, it is an insulator); metals have low “s” values-they are good conductors