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chem 1331 midterm 3
Terms in this set (86)
One mole of an ideal gas is expanded from a volume of 1.00 liter to a volume of 8.41 liters against a constant pressure of 1.00 atm. How much work (in joules) is performed on the surroundings?
When an exothermic reaction is carried out in a coffee-cup calorimeter, what statement is correct?
The enthalpy of the products is lower than that of the reactants.
A system absorbs 159 kJ of heat, and performs 84 kJ of work on the surroundings. What is E of the system?
Given the thermochemical equation: 2SO2 + O2 --> 2SO3 . H = -198 kJ. How much heat is evolved when 320g of SO2 is burned?
30.0 mL of pure water at 282 K is mixed with 50.0 mL of pure water at 343 K. What is the final temperature of the mixture?
A 3.36 g sample of sucrose, C6H12O6 (180.2 g/mol) was burned in a bomb calorimeter to form CO2 and H2O. The heat capacity of the calorimeter itself was 876 J/K and it contained 803.1 g of water (c = 4.184 J/gK). If the temperature increased by 1.4 C, what is E (in kJ) for the combustion of 1 mole of sucrose?
Calculate the H for Ca + (1/2)O2 + CO2 => CaCO3
Use the following data to calculate the standard heat (enthalpy) of formation, H, of manganese(IV) oxide, MnO2
The following statements concerning petroleum are all true except:
All of its hydrocarbon chains contain the same number of carbon atoms.
Convert the following: 35.5 cm Hg to atm
A metal cylinder with a volume of 3.72 L can withstand a maximum pressure of 100 atm. What is the largest mass of oxygen gas (g) that can be safely stored in the cylinder (without bursting) at 35.4 C?
CaC2 reacts with water to give acetylene gas and calcium hydroxide. Write the balanced equation for the reaction. Assuming complete reaction, what volume (L) of acetylene (C2H2) forms at STP when 2.73 g CaC2 reacts with excess water.
A sample of 0.186 g of an ideal gas occupies 0.750 L at STP. What is the molar mass of the gas?
A 919.3 mL sample of hydrogen gas was collected over water at 25 C and a pressure of 681 torr. If the pressure of water vapor is 24.0 torr at 25.0 C, what mass of hydrogen gas was collected?
Consider three 5-L flasks, fixed with pressure gauges and small valves, each contain 4 g of gas at 273 K. Flask A contains H2, flask B contains He, and flask C contain CH4. Compare the flasks' contents in terms of the characteristics listed.
Flask A = Flask B = Flask C
Which of the following changes will NOT affect the total pressure of gas in a container, assuming all other factors remain constant?
Half of the molecules are replaced by an equal number of molecules of a gas with a different molecular weight.
Order the intermolecular forces (dipole-dipole, London dispersion, and hydrogen-bonding) from weakest to strongest.
London dispersion, dipole-dipole, hydrogen-bonding
As pure molecular solids, which of the following exhibits dipole-dipole intermolecular forces: HBr, NBr3, SBr2, and CBr4?
HBr, NBr3, and SBr2.
Which equation represents the number of atoms in a face-centered cubic unit cell?
# atoms = (1/2)(6) + (1/8)(8)
Metallic behavior of the elements is generally associated with
elements with low ionization energies.
What is the kinetic energy of a 2.17-kg object moving at 85.0 km/hr?
6.05 × 10^2 J
A gas absorbs 75 kJ of heat and does 32 kJ of work. Calculate ΔE for the gas.
For which one of the following reactions will ΔH be approximately (or exactly) equal to ΔE?
H2(g) + Br2(g) → 2HBr(g)
A 16.2 g piece of aluminum (which has a molar heat capacity of 24.03 J/°C•mol) is heated to 82.4°C and dropped into a calorimeter containing water (specific heat capacity of water is 4.18 J/g°C) initially at 22.3°C. The final temperature of the water is 25.7°C. Ignoring significant figures, calculate the mass of water in the calorimeter.
A fuel-air mixture is placed in a cylinder fitted with a piston. The original volume is 0.290-L. When the mixture is ignited, gases are produced and 865 J of energy is released. To what volume will the gases expand against a constant pressure of 635 mmHg, if all the energy released is converted to work to push the piston?
Given the heats of the following reactions:
I. P4(s) + 6Cl2(g) → 4PCl3(g)
II. P4(s) + 5O2(g) → P4O10(s)
III. PCl3(g) + Cl2(g) → PCl5(g)
IV. PCl3(g) + O2(g) → Cl3PO(g)
Calculate the value of ΔH for the reaction below:
P4O10(s) + 6PCl5(g) → 10Cl3PO(g)
• C2H4(g) + 3O2(g) => 2CO2(g) + 2H2O(l) ΔHf = -1411 kJ
• C(s) + O2(g) => CO2(g) ΔHf = -393.5 kJ
• H2(g) + 1/2O2(g) => H2O(l) ΔHf = -285.8 kJ
Use the data given above to find the standard enthalpy of formation of ethylene, C2H4(g)
The combustion of hydrogen gas releases 286 kJ per mol of hydrogen. If 11.0 L of hydrogen at STP was burned to produce electricity, how long would it power a 100-watt (W) light bulb? Assume no energy is lost to the surroundings. (1 W = 1 J/s)
A 0.850-mole sample of nitrous oxide, a gas used as an anesthetic by dentists, has a volume of 20.46 L at 123°C and 1.35 atm. What would be its volume at 468°C and 1.35 atm?
What mass of Ar gas (in g) is contained in a 5 L tank in which its pressure is 0.303 atm and the temperature is 67.7°C?
Methane, CH4(g), reacts with steam to give synthesis gas, a mixture of carbon monoxide and hydrogen. CH4(g) + H2O(g) => CO(g) + H2(g) [unbalanced]
• What mass of hydrogen is formed if 275 L of methane (measured at STP) is converted to synthesis gas?
A 1.325 g sample of an unknown vapor occupies 368 mL at 114°C and 946 mmHg. The simplest formula of the compound is NO2. Which could be the molecular formula of the compound?
What is the volume occupied at STP by a mixture of 4.00 g of He(g), 2.00 g of H2(g) and 32.0 g of O2(g)?
Which of the following is not true of an ideal gas?
The mass of the gas particles is negligible.
Under which of the following sets of conditions will a real gas deviate most (act most differently) from ideal behavior?
small volume, low temperature, high pressure
Which of the following properties of water can be attributed to hydrogen bonding?
1. high melting point
2. high heat of vaporization
3. large deviations from ideal gas behavior in the gas phase
4. high surface tension
1, 2, 3, and 4
• An atom located on a face of a unit cell is shared equally between ____ unit cells.
Which of the following best describes the bonding between atoms in metals.
the valence electrons of each metal atom are delocalized over all of the atoms in the piece of metal
One mole of an ideal gas is expanded from a volume of 1.00 liter to a volume of 8.41 liters against a constant external pressure of 1.00 atm. How much work (in joules) is performed on the surroundings? Ignore significant figures for this problem. (T = 300 K; 1 L•atm = 101.3 J)
A quantity of water was vaporized completely in a piston-cylinder apparatus at 100oC against a constant pressure of 1.00 atm. During the process, 22.6 kJ of heat flowed into the system which did 1.70 kJ of work on the surroundings. What is the enthalpy change of the system?
Consider the combustion of ethyl alcohol:
• C2H5OH(l) + 3O2(g) => 2CO2(g) +3H2O(l), ΔH = -1.37 x 103 kJ
When a 15.1 g sample of ethyl alcohol is burned as above, how much heat is released?
4.49 x 10^2 kJ
A 46.0 g sample of a metal is heated to 95.0°C and then placed in a calorimeter containing 120.0 g of water (c = 4.18 J/g°C) at 21.6°C. The final temperature of the water is 24.5°C. Which metal was used?
Iron (c = 0.45 J/g°C)
A 2.62 g sample of sucrose, C6H12O6, (180.2 g/mol) was burned in a bomb calorimeter to form CO2 and H2O. The heat capacity of the calorimeter itself was 876 J/K and it contained 885.2 g of water (c = 4.184 J/g.K). If the temperature increased by 1.3°C, what is ΔE (in kJ) for the combustion of 1 mole of sucrose? Enter your answer with two decimal places and no units. Hint:calculate q first then ΔE.
Calculate ΔHrxn for NOCl(g) => 1/2N2(g) + 1/2O2(g) + 1/2Cl2(g) given the following set of thermochemical equations:
• N2(g) + O2(g) => 2NO(g) ΔHrxn = +180.6 kJ
• NO(g) + 1/2Cl2(g) => NOCl (g) ΔHrxn = -38.6 kJ
The heat of formation of Fe2O3(s) is -826.0 kJ/mol. Calculate the heat of the reaction below when a 27.86-g sample of iron is reacted.
• 4Fe(s) +3O2(g) ---> 2Fe2O3(s)
Which of the following is both a greenhouse gas and a fuel?
If 3.21 mol of an ideal gas occupies 56.2 L at 44 oC and 1130 torr, what volume will 5.29 mol of this gas occupy under the same conditions?
A 13.1 L balloon is filled with H2(g) at 60.13 oC producing a pressure of 1.23 atm. Assuming that the balloon can expand or contract over a sufficient range of volume, what is its volume in L when the temperature is 146.9 oC and the pressure is 1,642 torr? Enter your answer with two decimal places and no units.
If 2.56 g of an unknown gas occupies a volume of 111 mL at 753 torr and 22 °C, what is the molar mass of the gas?
Small quantities of hydrogen can be prepared by the addition of hydrochloric acid to zinc. A sample of 195 mL of hydrogen was collected over water at 25°C and 753 torr. What mass of hydrogen was collected? (Pwater = 24 torr at 25°C)
Four identical 1.0-L flasks contain the gases He, Cl2, CH4, and NH3, each at 0°C and 1 atm pressure.
• For which gas do the molecules have the highest average velocity?
Propane, C3H8, will behave most like an ideal gas:
at high temperature and low pressure
Which one of the following decreases as the strength of the attractive intermolecular forces increases?
ideal gas behavior
What is responsible for capillary action, a property of liquids?
two of these
Which of the following statements concerning the cubic unit cell is/are CORRECT?
1, 2, and 3
Which of these is least characteristic of metals?
When a system performs work on the surroundings, the work is reported with a negative sign.
An endothermic reaction is carried out in a coffee-cup calorimeter. Which statement is incorrect for this process?
The temperature of the water decreases.
A system initially has an internal energy E of 501 J. It undergoes a process during which it releases 111 J of heat energy to the surroundings, and does work of 222 J. What is the final energy of the system, in J?
Exactly 248.0 J will raise the temperature of 10.0 g of a metal from 25.0°C to 60.0°C. What is the specific heat capacity of the metal?
A bomb calorimeter has a heat capacity of 2.47 kJ/K. When a 0.105-g sample of ethylene (C2H4) was burned in this calorimeter, the temperature increased by 2.14 K. Calculate the energy of combustion for one mole of ethylene.
-1.41 × 103 kJ/mol
Consider the following numbered processes:
1. • A → 2B
2. • B → C + D
3. • E → 2D
ΔH for the process A → 2C + E is
ΔH1 + 2ΔH2 - ΔH3
This fossil fuel was formed from the remains of plants that were buried and exposed to high pressure and heat over time.
Convert the following: 1.1 atm to kPa
Suppose that 8.61 mol of hydrogen gas occupies a 31.6 L steel tank. At what temperature in °C will the pressure in the tank be 1,185 torr?
In the reaction below, what volume of PCl5(g) will be produced by the reaction of 15.4 L of chlorine gas with excess phosphorus (P4) if all gas volumes are measured at STP?
• P4(g) + Cl2(g) => PCl5(g)(unbalanced)
A chemistry student found the density of Freon-11 (CFCl3) to be 5.58 g/L under her experimental conditions. Her measurements showed that the density of an unknown gas was 4.38 g/L under the same conditions. What is the molar mass of the unknown?
A 1.0 mole sample of He is placed in an empty vessel to create a presure of 0.5 atm. A 32 g quantity of CH4 is added to the vessel. The TOTALpressure in the container will be _____________.
Consider three 5-L flasks, fixed with pressure gauges and small valves, each contain 4 g of gas at 273 K. Flask A contains H2, flask B contains He, and flask C contains CH4. Compare the flasks' contents in terms of the characteristics listed.
Flask A > Flask B > Flask C
Select the gas with the highest average kinetic energy per mole at 298 K.
All have the same average kinetic energy.
Which best explains the following trend?
Element • b.p. (K)
none of these
Which of the following statements is(are) correct?
The system does work on the surroundings when an ideal gas expands against a constant external pressure.
Consider the reaction:
H2 + (1/2) O2 => H2O H=-286 kJ
Which of the following is true?
Both A and C are true.
The coal with the highest energy available per unit burned is
Which of the following is not a postulate of the kinetic molecular theory?
Gas particles have most of their mass concentrated in the nucleus of the atom.
One of the characteristics of real gas molecules is that they attract one another. Which of these characteristics of gases best supports this notion?
Non-ideal gas behavior of real gases is often observed at low temperature
Which of the following pollutant gases is not produced directly in a combustion engine?
In which substance would the dispersion forces be the weakest?
Arrange the three common unit cells in order from least dense to most dense packing
primitive cubic < body-centered cubic < face-centered cubic
In which of these substances are atoms held together by metallic bonding?
Arrange Cl2, ICl, and Br2 in order from lowest to highest boiling point.
Cl2 < Br2 < ICl
How many unit cells share an atom which is located at a corner (or lattice point) of a unit cell?
According to the first law of thermodynamics, the energy of the universe is constant. Does this mean that E is always equal to zero?
No, E does not always equal zero because it refers to the system's internal energy, which is affected by heat and work.
All of the following are postulates of the kinetic-molecular theory except:
At a constant temperature, each molecule has the same kinetic energy.
Liquids with large intermolecular forces tend to have a high surface tension.
If a metal crystallizes in a primitive cubic lattice, each metal atom has ___ nearest neighbor atoms of the same kind.
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