chapter 10- equilibria and equilibrium constant

Which is an example of the chemical nature of substances affecting the rate of reaction? -Sodium oxidizes overnight whereas iron takes much longer -Large pieces of iron react slowly with acids while finely divided iron reacts more rapidly -Food spoils more quickly on the kitchen counter than in the fridge all of the above

Sodium oxidizes overnight whereas iron takes much longer

A small amount of product is removed from a system at equilibrium. Which of the following will change? Select all that apply. -The amount of reactants -The value of the equilibrum constant -The value of Q -The temperature associated with the equilibrium constant describing this system

The amount of reactants The value of Q

Identify the options below that are results of decreasing the temperature of a system that includes an exothermic reaction in the forward direction. The concentrations of the reactants increase. The concentrations of the products increase. The equilibrium shifts toward the products. The equilibrium constant decreases.

The concentrations of the products increase. The equilibrium shifts toward the products.

The rate at which a reaction is proceeding at a specific point in time is called the:

Instantaneous rate

Which is an example of the state of subdivision of the reactants affecting the rate of reaction? -A reaction proceeds more quickly in the laboratory when placed over a Bunsen burner -A reaction slows down as it proceeds calcium reacts with water moderately, sodium reacts with water explosively large pieces of iron react slowly with acids while finely divided iron reacts more rapidly

large pieces of iron react slowly with acids while finely divided iron reacts more rapidly

If the forward reaction of an equilibrium is endothermic, the ΔH will have a _______ sign, and the heat can be thought of as a ________

positive, reactant

Which of the following concentrations appear in the numerator of the equilibrium constant expression? Select the correct answer below: -solid -reactant -product -gas

product

The first postulate of collision theory states that the rate of a reaction is _______ to the rate of reactant collisions.

proportional

An increase in temperature will cause an equilibrium to: shift right shift left no change depends on the equilibrium

depends on the equilibrium

The rate at which a reaction proceeds when the reaction first commences is called the:

initial rate

Which of the following demonstrate homogeneous equilibria? (select all that apply) -A reaction involving both gases and liquids -A reaction occurring in a liquid-phase solution -A reaction involving exclusively gaseous species -A reaction between solutes in liquid solution

-A reaction occurring in a liquid-phase solution -A reaction involving exclusively gaseous species -A reaction between solutes in liquid solution

Which description best fits the definition of activated complex? -An activated complex is a catalyst present in a different phase from the reactants -An activated complex is a catalyst present in the same phase as the reactants -An activated complex is a molecule or ion produced in one step of a reaction mechanism and consumed in another -An activated complex is an unstable combination of reactant species representing the highest energy state of a reaction system.

-An activated complex is an unstable combination of reactant species representing the highest energy state of a reaction system.

Which of the following react relatively slowly (hours to years) rather than nearly instantaneously? (select all that apply) -An egg spoiling in a freezer -Calcium exposed to water -Iron train tracks exposed to the air -small pieces of elemental sodium exposed to air

-An egg spoiling in a freezer -Calcium exposed to water -Iron train tracks exposed to the air

An equilibrium constant is described by which of the following? -An equilibrium constant is equal to the molar concentrations of the products multiplied by those of the reactants, with each concentration being raised to the power equal to the coefficient in the equation. -An equilibrium constant is the constant used to scale an equilibrium reaction such that it expresses the formation of exactly 1 mol of product. -An equilibrium constant is the sum of the concentrations or partial pressures of components of a reaction at equilibrium. -An equilibrium constant is the value of the reaction quotient for a system at equilibrium.

-An equilibrium constant is the value of the reaction quotient for a system at equilibrium.

Identify the options below that are false about chemical equilibria. (select all that apply) -There is no net change in the concentrations of the reactants and products. -Concentrations of products and reactants oscillate between a set range of values. -The relative amounts of the reactants and products may not necessarily be equal. -At equilibrium, all species have stopped reacting altogether.

-Concentrations of products and reactants oscillate between a set range of values. -At equilibrium, all species have stopped reacting altogether.

Which of the following are postulates of collision theory? -The rate of a reaction is proportional to the rate of effective reactant collisions. -The reacting species must collide with the optimal orientation to allow the appropriate bonds to break and/or form as reactants are converted to products. -Each collision of reacting atoms results in product formation. -The collision must occur with adequate energy to permit mutual penetration of the reacting species' valence shells so that the electrons can rearrange and form new bonds.

-The rate of a reaction is proportional to the rate of effective reactant collisions. -The reacting species must collide with the optimal orientation to allow the appropriate bonds to break and/or form as reactants are converted to products. -The collision must occur with adequate energy to permit mutual penetration of the reacting species' valence shells so that the electrons can rearrange and form new bonds. (Collision theory relies on three postulates. First, the rate of a reaction is proportional to the rate of reactant collisions. Second, the reacting species must collide in an orientation allowing contact between the atoms that will bond together in the product. And lastly, the collision must occur with enough energy to enable the penetration of valence shells so that electrons rearrange to form new bonds.)

Choose the options below that are true of chemical equilibria. (select all that apply) Select all that apply: -The reaction proceeds in the forward and reverse directions at the same rate. -Both the forward and the reverse reactions are achievable. The relative amounts of all species must be different. There is no net change in concentrations of reactants and products.

-The reaction proceeds in the forward and reverse directions at the same rate. -Both the forward and the reverse reactions are achievable. -There is no net change in concentrations of reactants and products.

Of the following, which are true of chemical equilibria? (select all that apply) -At equilibrium, all reaction species must have a concentration value of 1 M or a partial pressure of 1 atm. --The reaction proceeds in the forward and reverse directions simultaneously. -The amounts of all products and all reactants must be equal at equilibrium. -The forward and reverse reactions occur at equal rates.

-The reaction proceeds in the forward and reverse directions simultaneously. -The forward and reverse reactions occur at equal rates.

An ICE chart is needed to calculate Kc if: -only equilibrium concentrations are given -only initial concentrations are given -a combination of initial and equilibrium concentrations are given -all of the above

-a combination of initial and equilibrium concentrations are given

Which is an example of the chemical nature of substances affecting the rate of reaction? -a reaction proceeds more quickly in the laboratory when placed over a Bunsen burner -a solution containing two moles of each reactant has a faster instantaneous rate of reaction than a solution of the same volume with only one mole of each reactant -calcium reacts with water moderately, sodium can react explosively with water -large pieces of iron react slowly with acids while finely divided iron reacts more rapidly

-calcium reacts with water moderately, sodium can react explosively with water (The difference in rate of reaction between calcium and sodium in water is due to the difference in chemical identity between sodium and calcium. The remaining choices address differences in rate due to temperature (choice a), concentration (choice b), and surface area (choice d).)

Identify the options below that are examples of concentrations of reactants affecting the rate of a reaction. (select all that apply) -Calcium reacts at a moderate rate with water to form hydrogen and a base, whereas sodium reacts in a similar way in mere seconds. -A 5 M sample of hydrogen peroxide decomposes at a faster rate than a 2 M sample of the same volume. -Calcium carbonate deteriorates more rapidly in polluted air than in clean air. -Finely ground table salt reacts with sulfur dioxide more quickly than small chunks of salt in a grinder.

A 5 M sample of hydrogen peroxide decomposes at a faster rate than a 2 M sample of the same volume. Calcium carbonate deteriorates more rapidly in polluted air than in clean air.

Which is an example of concentration affecting the rate of reaction?

A reaction slows down as it proceeds.

Of the following, which is a false statement regarding chemical equilibrium? -All reactions are reversible in theory, but it is not always feasible to produce conditions that lead to any significant formation of reactants from the products. -Some reactions favor the forward direction so much over the reverse direction that they proceed until consuming nearly all of the reactants. -A reversible reaction means a reaction that is at equilibrium between reactants and products. -A reversible reaction that is in a state of equilibrium between reactants and products is running in both the forward and reverse directions at the same rate.

A reversible reaction means a reaction that is at equilibrium between reactants and products.

Which of the following illustrates how the intrinsic chemical properties of a reactant affect reaction rate? (select all that apply)

Calcium reacts with water at a moderate rate to form hydrogen gas and a base, whereas sodium reacts in a similar way in mere seconds. A wooden headboard burns more quickly in a fire than an iron headboard. Phosphorus burns much more rapidly in an atmosphere of pure oxygen than in air. Zinc dust reacts more rapidly with hydrochloric acid than a large solid piece of zinc.

Which of the following decreases the rate of a reaction? -Decreasing the concentration of a reactant that does not appear in the rate law -Heating up the reaction vessel on a hot plate -Taking a break after continuously stirring a very slow reaction for half an hour -Decreasing the concentration of a first order reactant

Decreasing the concentration of a first order reactant

-The law of mass action best fits which of the following descriptions? -The law of mass action is the statement that a chemical system returns to equilibrium after a disturbance. -The law of mass action is a model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics. -The law of mass action is the statement that the partial pressure exerted by a solution component is equal to the product of the component's mole fraction in the solution and its equilibrium vapor pressure in the pure state. -The law of mass action is the statement that the reaction quotient remains constant when a reversible reaction has attained equilibrium at a given temperature.

The law of mass action is the statement that the reaction quotient remains constant when a reversible reaction has attained equilibrium at a given temperature.

Which is an example of the state of subdivision of the reactants affecting the rate of reaction? -The smaller the piece of wood, the faster it burns -Food spoils more quickly on the kitchen counter than in the fridge -A reaction slows down as it proceeds -Calcium reacts with water moderately, sodium reacts with water explosively

The smaller the piece of wood, the faster it burns (The smaller pieces of wood have greater surface area available for combustion and thus the rate of reaction is influenced by subdivision. The rate of reaction in the other examples are influenced by temperature (choice b), concentration (choice c), and chemical nature (choice d).

Changing the temperature of a system at equilibrium: -shifts the reaction quotient away from the equilibrium value -increases the rate of reaction -changes the value of the equilibrium constant -it depends on the equation

changes the value of the equilibrium constant

K is always __________.

dependent on the reaction

A chemical reaction is at equilibrium. In which of the following circumstances would a change in temperature be least likely to affect the equilibrium of a chemical reaction? rate of the forward reaction rate of the reverse reaction equilbrium constant none of the above

equilbrium constant A change in temperature will affect the equilibrium constant, which is what causes the equilibrium to shift, so that the equilibrium concentrations can reflect the new value for Kc

A catalyst will: -increase the change in enthalpy of a reaction -decrease the change in enthalpy of a reaction -have no effect on the change in enthalpy of a reaction -depends on the reaction

have no effect on the change in enthalpy of a reaction A catalyst only affects the energy of the transition state, it will have no impact on the change in enthalpy for the overall reaction.

When converting between Kc and Kp, this relationship will depend on the change in:

moles of gas between reactants and products

If an equilibrium reaction is exothermic in the forward direction, the change in enthalpy of the reaction will have a _______ sign, and the heat produced in the forward reaction can be listed as a _________.

negative, product

If products are removed from a system at equilibrium, the equilibrium will: shift right shift left no change depends on the equilibrium

shift right If products are removed, the equilibrium will shift right to try to regenerate some of the products and regain equilibrium.

Kc expressions will exclude: -gases -aqueous substances -solids none of the above

solids

dentify the options below that are results of decreasing the temperature of a system that includes an exothermic reaction in the forward direction. Select all that apply: The concentrations of the reactants increase. The concentrations of the products increase. The equilibrium shifts toward the products. The equilibrium constant decreases.

the concentrations of the products increase the equilibrium shifts toward the products

Which of the following is true about the rate expressions in a chemical reaction?

the rate expression for any product will be positive, and that for any reactant will be negative Reactants are used up during a reaction, so the change in their concentrations as time moves forward is negative, giving a negative rate expression. Conversely, products are produced during a reaction, so the change in their concentrations as time moves forward is positive, giving a positive rate expression.

If a stress causes the value of Q to increase, what will happen to the system? the rate of the forward reaction will increase the rate of the reverse reaction will increase the system will expand the system will contract

the rate of the reverse reaction will increase

When is the average rate of a reaction equal to its instantaneous rate at a given second?

when the reaction proceeds at a constant rate