Stoichiometry and the Mole
Given the balanced equation representing a reaction: 2KClO3 + energy→2KCl + 3O2
Given the balanced equation representing a reaction: 2KClO3 + energy→2KCl + 3O2
What is the mass of KCl produced when 24.51 grams of KClO3 reacts completely to produce 9.60 grams of O2?
Hint: ChEM!
(1) 5.31 g (2) 14.91 g
(3) 34.11 g. (4) 43.71 g
(2)
24.51g = 9.60g + x
x = 14.91 g
At STP, which property would be the same for 1.0 liter of helium and 1.0 liter of argon?
(1) boiling point (2) density
(3) mass (4) number of atoms
Think Avacado's law
4
Which is one term used to express the concentration of an aqueous solution?
(1) parts per million (2) heat of fusion
(3) pressure at 0°C (4) volume at 0°C
1
What is the number of electrons shared between the two atoms in an O2 molecule?
(1) 6 (2) 2 (3) 3 (4) 4
4
2 electrons per bond
2 bonds
(1) lower entropy (lower disorder) and lower energy
(2) higher entropy (higher disorder) and lower energy
(3) lower entropy (lower disorder) and higher energy
(4) higher entropy (higher disorder) and higher energy
2
Given the balanced equation for the reaction of butane and oxygen:
2C4H10 + 13O2 → 8CO2 + 10H2O + energy
How many moles of carbon dioxide are produced when 5.0 moles of butane react completely?
(1) 5.0 mol (2) 10. mol
(3) 20. mol (4) 40. mol
(3)
given: Unknown
5.0 moles C4H10 moles CO2 made?
8 CO2 = 2 C4H10
According to the kinetic molecular theory, which statement explains why an ideal gas can be compressed to a smaller volume?
(1) The motion of the gas particles is circular and orderly.
(2) The force of attraction between the gas particles is strong.
(3) As the gas particles collide, the total energy of the system decreases.
(4) The gas particles are separated by great distances relative to their size.
4. The uniqueness of gases and why they behave differently than other states of matter with respect to changing factors like temperature and pressure (solubility, rate of reaction) is largely due to their particulate structure or lack their of!
Based on Table G, what is the mass of KCl that must be dissolved in 200. grams of H2O at 10.°C to make a saturated solution?
(1) 15g (2) 30. g (3) 60.g (4) 120. g
(3)
100 g is 30 we have twice that amount of water
What is the vapor pressure of propanone at 45°C?
(1) 21 kPa (2) 60. kPa (3) 70. kPa (4) 79 kPa
Which terms represent two categories of compounds?
(1) chemical and physical
(2) chemical and molecular
(3) ionic and physical
(4) ionic and molecular
4
One mole of bromine gas, Br2 (g), has a mass of?
a) 79.9 amu b) 79.9 g
c) 159.8 amu d) 159.8 g
d
Under which conditions of temperature and pressure does a sample of propane behave least like an ideal gas?
(1) 250. K and 1.0 atm. (2) 250. K and 5.0 atm
(3) 500. K and 1.0 atm (4) 500. K and 5.0 atm
2
PLIGHT means it will be most like an ideal gas, we want the opposite of these conditions!
Compared to the freezing point and boiling point of water at 1.0 atm, a 0.5 M aqueous solution of NaCl at 1.0 atm has
(1) a lower freezing point and a lower boiling point
(2) a lower freezing point and a higher boiling point
(3) a higher freezing point and a lower boiling point
(4) a higher freezing point and a higher boiling point
2
adding solute makes properties more extreme
water will have a higher freezing point and lower bp
a solution with other stuff mixed in will be harder to change phase
An atom of which element bonds with an atom of hydrogen to form the most polar bond?
Hint, why guess when you have Table S?
(1) bromine (2) chlorine
(3) fluorine (4) iodine
3
biggest electronegativity difference
<.5 = nonpolar (equal sharing of e- in bond)
> .5 < 2 = polar covalent bond (unequal sharing of e- in bond)
>2 = ionic
A solid sample of copper is an excellent conductor of electric current. Which type of chemical bonds are in the sample?
(1) metallic (2) ionic
(3) polar covalent (4) nonpolar covalent bonds
1
Given the UNbalanced equation below, what are the molar coefficients using the smallest whole-number coefficients if the equation were balanced?
Hint: R & P!
Pb(NO3)2 (aq) + KI (aq) -> PbI2 (s) + KNO3 (aq)
Pb(NO3)2 (aq) + 2KI (aq) -> PbI2 (s) + 2KNO3 (aq)
A rigid cylinder with a movable piston contains a sample of hydrogen gas. At 330. K, this sample has a pressure of 150.kPa and a volume of 3.50L. What is the volume of this sample at STP?
Ideal Gas Law! Table T
(1) 0.233 L (2) 1.96 L
(3) 4.29 L (4) 6.26 L
(3)
Given...
P1=150.kPa P2=101.3 kPa
V1=3.50L. V2=?
T1= 330. K T2=273 K
Based on Table G, which sample, when added to 100. grams of water and thoroughly stirred, produces a heterogeneous mixture at 20.°C?
(1) 20. g of KCl (2) 20. g of KI
(3) 80. g of KCl (4) 80. g of KI
heterogeneous = code for not evenly blended - look for something that will have solid in it - either an INSOLUBLE compound OR a SUPERSATURATED Solution
3
Which phrase describes the molecular polarity and distribution of charge in a molecule of carbon dioxide, CO2 and NH3?
(1) Both are nonpolar molecules with even distribution of charge
(2) Both are polar molecules with uneven distribution of charge
(3) CO2 is nonpolar - even distribution of charge NH3 is polar - uneven distribution of charge
(4) CO2 is polar - uneven distribution of charge NH3 is nonpolar - even distribution of charge
(3)
molecular polarity deals with how charge is distributed over the whole molecule
Which factor affecting reaction rates is NOT correctly matched with its mechanism?
(1) increasing temperature - increases frequency of collisions thus increases reaction rate
(2) increasing surface area - increases frequency of collisions thus increases reaction rate
(3) decreasing concentration - decreases frequency of collisions thus decreases (slows) reaction rate
(4) increasing pressure - increases frequency of collisions and affects GASES ONLY - thus increases reaction rates
(5) catalyst: increases potential energy of reactants by opening up a new pathway thus increasing reaction rate
5) catalysts LOWER the ACTIVATION ENERGY (dashed line under the hump in POTENTIAL ENERGY DIAGRAMS)
catalysts DO NOT change the PE of products or reactants
catalysts DO NOT change the delta H (enthalpy) of the reaction (PE products - PE reactants)
The unbalanced equation below represents the reaction between silver sulfide and aluminum.
Ag2S + Al → Ag + Al2S3
Balance the equation in your answer booklet for the reaction, using the smallest whole number coefficients.
3Ag2S +2 Al → 6Ag + Al2S3
Compared to a sample of helium at STP, the same sample of helium at a higher temperature and a lower pressure
(1) condenses to a liquid
(2) is more soluble in water
(3) forms diatomic molecules
(4) behaves more like an ideal gas
(4)
increased temperature DECREASES gas solubility - gas particles already have high ke and have fast constant random motion, increasing their avg KE (increasing Temp) will only make them move further away from each other and more speedily and they're harder to trap
What is the concentration of an aqueous solution that contains 1.5 moles of NaCl in 500. milliliters of this solution?
(1) 0.30 M (2) 0.75 M (3) 3.0 M (4) 7.5 M
M = moles / liters
500ml/1000 = 0.500 L
M = 1.5 moles/0.500 L
M=3.0 M
3
Which substance is NOT correctly paired with its molecular polarity and strongest intermolecular force?
1) HCl - polar molecule - dipole-dipole forces
2) HF - polar molecule - hydrogen bonding
3) CH3OH - polar molecule - hydrogen bonding
4) CCl4 - polar molecule - LDF (london dispersion forces)
4
nonpolar molecule, LDFs!
Larger molar mass, greater LDFs
H bonding is FON (h bound to a F, O or N)
Ionization Energy is the energy needed to remove a valence electron..
Describe and explain the first ionization energy of elements in group I going as atomic number increases.
(1) IE increases going down a group as atomic number increases because there are more electrons and the nucleus pulls more on the valence electrons as the number of electrons goes up.
(2) IE decreases as you go down a group because the atomic radius increases because there are more electron shells. The nucleus has "less control" over the valence electrons making them easier to pluck off the atom and thus require less energy (less effort) to remove them. This is why Fr is the MOST reactive of the group I metals.
(3) IE increases as you go down a group because the atomic radius decreases meaning the nucleus can pull more on electrons and increase how much energy it takes to remove the valence electrons.
(4) IE increases as you go down a group because it takes more energy to remove a valence electron in bigger atoms.
2