Chemistry MCAT Unit 4

What is Newton's law of cooling?

A body's rate of cooling is proportional to the temperature difference between the body and its environment.

2SO2(g) + O2(g) ->/<- 2SO3(g) delta H=-198 kJ If the above reaction was at equilibrium inside a closed container, decreasing the volume of the container would cause which of the following? A) An increase in the formation of sulfur trioxide B) A decrease in the formation of sulfur trioxide C) No effect on the formation of sulfur trioxide D) The effect cannot be determined with the information provided.

A) An increase in the formation of sulfur trioxide

Which of the following does NOT describe enthalpy? A) Enthalpy of the universe remains constant. B) Enthalpy is a state function. C) Enthalpy is an extensive property. D) Like internal energy, enthalpy depends only on temperature for an ideal gas.

A) Enthalpy of the universe remains constant. Enthalpy of the universe does not remain constant because enthalpy is not conserved.

Which of the following statements is false? A) Higher emissivity indicates that a lower amount of radiation energy is absorbed. B) Lower emissivity indicates that a lower amount of radiation energy is absorbed. C) The fraction of absorbed radiation is indicated by its emissivity between 0 and 1. D) Dark colors tend to radiate and absorb better than light colors, which tend to reflect.

A) Higher emissivity indicates that a lower amount of radiation energy is absorbed.

Intensive properties are independent of the size of a system. Which of the following is an example of an intensive property? I. volume II. pressure III. temperature IV. moles A) II and III B) I and IV C) only IV D) I, II, III, IV

A) II and III

During the course of the dissociation of solid silver chloride into aqueous silver and aqueous chloride, both entropy and enthalpy are increased. If the reaction is not spontaneous at a given temperature and pressure, what can be done to make the reaction occur spontaneously? A) Increase the temperature. B) Decrease the temperature. C) Increase the pressure. D) Decrease the pressure.

A) Increase the temperature.

Which of the following statements about entropy is false? A) The entropy of a system will always increase in a spontaneous reaction. B) Entropy is a measure of disorder. C) The entropy change of a forward reaction is exactly opposite to the entropy change of the reverse reaction. D) Entropy increases with temperature.

A) The entropy of a system will always increase in a spontaneous reaction.

Sulfur dioxide reacts with oxygen in a reversible reaction to form sulfur trioxide (the enthalpy= -200 kJ/mol). If the temperature at which the reaction takes place is increased, which of the following will take place? A) The rates of both the forward and reverse reactions will increase. B) Only the rate of the forward reaction will increase. C) Only the rate of the reverse reaction will increase. D) The rates of neither the forward nor reverse reactions will increase.

A) The rates of both the forward and reverse reactions will increase.

Which of the following is a type of kinetic energy? A) Vibrational energy B) Chemical energy C) Rest mass energy D) Intermolecular energy

A) Vibrational energy

What is the Third Law of Thermodynamics?

Any pure element or compound in its solid form at absolute zero and internal equilibrium has zero entropy. (only a theory)

Extensive properties are proportional to the size of a system. Which of the following is an example of an extensive property? I. volume II. pressure III. temperature IV. moles A) II and III B) I and IV C) only I D) I, II, III, IV

B) I and IV

Atoms in a monoatomic gas do NOT have which components of kinetic internal energy? I. translational energy II. rotational energy III. vibrational energy A) I only B) II and III C) II only D) I and III

B) II and III

Which of the following are examples of path functions? I. temperature II. heat III. internal energy IV. work A) I and III B) II and IV C) I and II D) III and IV

B) II and IV

Which of the following statements is false? A) To find the reverse of a reaction, just look at the energy vs. reaction progress graph backwards. B) The forward and reverse of a reaction will have the same activation energy. C) The forward and reverse of a reaction will have the same change in enthalpy, just different signs. D) All of the above are false.

B) The forward and reverse of a reaction will have the same activation energy. The forward and reverse of a reaction will have different activation energies.

At constant pressure, the magnitude of PV work is equal to: A) change in temperature. B) change in volume. C) change in moles. D) none of the above

B) change in volume.

2SO2(g) + O2(g) ->/<- 2SO3(g) delta H=-198 kJ For the above reaction, which of the following will most increase the production of heat? A) high pressure and high temperature. B) high pressure and low temperature. C) low pressure and high temperature. D) low pressure and low temperature.

B) high pressure and low temperature.

The standard enthalpy of formation for liquid water is: -285.8 kJ/mol. Which of the following could be the standard enthalpy of formation for water vapor? A) -480.7 kJ/mol B) -285.8 kJ/mol C) -241.8 kJ/mol D) +224.6 kJ/mol

C) -241.8 kJ/mol

A catalyst increases the rate of a reaction without being consumed or permanently altered. Which of the following statements about catalysts is false? A) Catalysts increase the rate of the forward and reverse reactions. B) A catalyst may lower the activation energy and/or increase the steric factor. C) A catalyst can alter the equilibrium and the equilibrium constant of a reaction. D) A catalyst creates a different energy pathway.

C) A catalyst can alter the equilibrium and the equilibrium constant of a reaction.

All of the following are true concerning a reaction at equilibrium EXCEPT: A) The rate of the forward reaction equals the rate of the reverse reaction. B) There is no change in the concentrations of either the products or the reactants. C) The activation energy has reached zero. D) The Gibbs free energy has reached a minimum.

C) The activation energy has reached zero.

Which of the following is true concerning a reaction that begins with only reactants and moves toward equilibrium? A) The rates of the forward and reverse reactions decrease until equilibrium is reached. B) The rates of the forward and reverse reactions increase until equilibrium is reached. C) The rate of the forward reaction decreases and the rate of the reverse reaction increases until equilibrium is reached. D) The rate of the forward reaction increases and the rate of the reverse reaction decreases until equilibrium is reached.

C) The rate of the forward reaction decreases and the rate of the reverse reaction increases until equilibrium is reached.

All of the following are forms of internal energy EXCEPT: A) rotational energy. B) vibrational energy. C) gravitational energy. D) translational energy.

C) gravitational energy.

A reaction quotient of Q>K indicates that the reaction: A) will undergo a rightward shift to increase the concentration of products. B) has a forward reaction rate greater than the reverse reaction rate. C) has lower concentrations of reactants than the expected equilibrium concentrations. D) favors the formation of products over the formation of reactants.

C) has lower concentrations of reactants than the expected equilibrium concentrations.

Immediately upon bringing a hot piece of metal into a room, the heat is felt from 5 meters away. This heat transfer is probably occurring through: A) convection. B) transduction. C) radiation. D) conduction.

C) radiation.

Loss of three dimensional shape results in loss of protein function. Which of the following components of internal energy is responsible for denaturation? A) rotational energy B) intermolecular potential energy C) vibrational energy D) electronic energy

C) vibrational energy

A chemical cold pack contains a membrane separating water and ammonium nitrate. When the membrane is broken, the compounds react, cooling the mixture. At standard state, the equilibrium constant K: A) =0 B) =1 C) <1 D) >1

D) >1

Mutations in enzymes in the human body often lead to diseases in which there is an excessive buildup of an intermediate. Why might this be bad? A) Intermediates are usually only present in small quantities. B) Intermediates are products of one step of a reaction and are reactants of a later step in a multistep reaction. C) The excess amount could disrupt cellular equilibrium and harm intracellular organelles. D) All of the above.

D) All of the above.

As the temperature of hydrogen gas in a sealed container is increased, which of the following occurs? A) A decrease in the random translational energy, decreasing pressure. B) A decrease in the random translational energy, increasing the pressure. C) An increase in the random translational energy, decreasing pressure. D) An increase in the random translational energy, increasing pressure.

D) An increase in the random translational energy, increasing pressure.

Which of the following describes a reaction that is always spontaneous? A) Increasing enthalpy and increasing entropy B) Decreasing enthalpy and decreasing entropy C) Increasing enthalpy and decreasing entropy D) Decreasing enthalpy and increasing entropy

D) Decreasing enthalpy and increasing entropy

Which of the following are considered potential internal energy? I. intermolecular potential energy II. electronic energy III. rest mass energy A) I only B) I and III C) III only D) I, II, III

D) I, II, III

Which of the following gas properties is needed to calculate the work done by an expanding gas? I. The initial and final pressures II. The initial and final volumes III. The path followed during expansion A) I only B) II only C) I and II only D) I, II, and III

D) I, II, and III

Which of the following is true concerning an air conditioner that sits inside a thermally sealed room and draws energy from an outside power source? A) It will require more energy to cool the room than if part of the air conditioner were outside of the room. B) It will require more time to cool the room than if part of the air conditioner were outside the room. C) It will require less energy to cool the room than if part of the air conditioner were outside the room. D) It cannot cool the room on a permanent basis.

D) It cannot cool the room on a permanent basis.

In the condensation of water, water goes from a gas to a liquid. Which of the following will be positive for the condensation of water at 25 degrees Celsius and 1 atm? A) enthalpy (delta H) B) entropy (delta S) C) Gibbs free energy (delta G) D) None of the above

D) None of the above

For a particular reversible reaction, the forward process is exothermic and the reverse process is endothermic. Which of the following statements must be true about this reaction? A) The forward reaction will be spontaneous under standard conditions. B) The reverse reaction will be spontaneous under standard conditions. C) The activation energy will be greater for the forward reaction than for the reverse reaction. D) The activation energy will be greater for the reverse reaction than for the forward reaction.

D) The activation energy will be greater for the reverse reaction than for the forward reaction.

A rigid container of constant volume is used to store compressed gas. When gas is pumped into the container, the pressure of the gas inside the container is increased and the temperature of the container also increases. Which statement is true of the work done on the container? A) The work is equal to the increase in the pressure inside the container. B) The work is equal to the increase in the temperature inside the container. C) The work is equal to the sum of the pressure and temperature increases. D) There is no work done on the container.

D) There is no work done on the container.

2SO2(g) + O2(g) ->/<- 2SO3(g) delta H=-198 kJ During the formation of sulfur trioxide, an increase in temperature would result in: A) a decrease in the equilibrium concentration of oxygen. B) an increase in the equilibrium concentrations of products. C) no change in equilibrium concentrations. D) a decrease in the equilibrium concentration of sulfur trioxide.

D) a decrease in the equilibrium concentration of sulfur trioxide.

Which of the following may increase the reaction rate? A) increasing the temperature of the liquid B) stirring the liquid C) shaking the liquid D) all of the above

D) all of the above

Which of the following is not included in internal energy? A) intermolecular potential energy B) electronic energy C) translational energy D) bond enthalpy

D) bond enthalpy

True or false, vibrational energy is present in monoatomic gases.

False, atoms in a monoatomic gas have no vibrational energy because they have no covalent bonds around which to vibrate.

True or false, entropy is a state function but enthalpy is not.

False, both enthalpy and entropy are state functions.

True or false, the difference between energy transfer defined as heat and energy transfer defined as work is that heat causes ordered molecular collisions.

False, heat causes random molecular collisions and work causes ordered molecular collisions.

True or false, solids and pure liquids should be included in the Law of Mass Action.

False, solids and pure liquids should NOT be included in the Law of Mass Action.

True or false, state functions are path dependent.

False, state functions are path independent.

True or false, steps before the slow step do not contribute to the rate law, but steps after the slow step do contribute to the rate law.

False, the steps before the slow step DO contribute to the rate law, but steps after the slow step DO NOT contribute to the rate law.

True or false, there is only one way to transfer energy between systems, which is through heat.

False, there are two ways to transfer energy between systems: heat and work.

What is the Second Law of Thermodynamics?

The entropy of an isolated system will never decrease (without some outside intervention, namely work)

What is the Law of Mass Action?

The mathematical relationship between a chemical equation and the associated equilibrium constant. K=[C]^c[D]^d/[A]^a[B]^b

What is Hess's Law of Heat Summation?

The sum of the enthalpy changes for each step is equal to the total enthalpy change regardless of the path chosen

What is the First Law of Thermodynamics?

The total energy of the system and surroundings is always conserved.

True or false, a catalyst affects the rate of a reaction but not the overall change in energy between products and reactants.

True

True or false, internal energy may be referred to as heat energy or thermal energy.

True

True or false, kinetics is governed by activation energy (the top part of a reaction energy diagram) and thermodynamics is governed by Gibbs Free energy (the bottom part of a reaction energy diagram).

True

True or false, radiation is the only type of heat transfer that can occur through a vacuum and does not require a medium.

True

True or false, the area under a pressure vs. volume graph is equal to the magnitude of work done.

True

True or false, the reactant's influence on reaction rate must be determined experimentally.

True

True or false, reaction rates can be enhanced by increasing the surface area of a catalyst.

True, this can be done by grinding a solid into a powder.

What is the zeroth law of thermodynamics?

Two systems in thermal equilibrium with a third system are in equilibrium with each other.