HwK 9

What is the basic postulate of collision theory?

The rate of a reaction is proportional to the number of collisions per second among the reactants.

What two factors influence the effectiveness of molecular collisions in producing chemical change?

The kinetic energy of the reactants in relation to the activation energy.

and

The orientation of the reactants.

In terms of the kinetic theory, why does an increase in temperature increase the reaction rate? Select the single best answer.

An increase in temperature means that a larger fraction of the reactant molecules possess the minimum energy necessary to surpass Ea.

What does the transition state theory attempt to describe about chemical reactions?

It describes chemical reactions in terms of the energy of the reaction.

What meaning do the terms reactants and products have when describing a chemical equilibrium?

Reactants are the substances to the left and products are the substances to the right of the double arrow.

Which of the following is a statement of Le Châtelier's principle?

When a system at equilibrium is disturbed so that the equilibrium is upset, the system changes in a way that opposes the disturbance and returns the system to a state of equilibrium.

Why doesn't a catalyst affect the position of equilibrium in a chemical reaction? Select all that apply.

The catalyst affects the rate of both the forward and reverse reactions to the same extent.

The ratio of the catalyzed forward and catalyzed reverse rates is the same as the ratio of the uncatalyzed forward and uncatalyzed reverse rate.

Which of the following compounds are likely to be electrolytes? Select all that apply.

CuBr2

iron(II) chloride

(NH4)2SO4

How did Arrhenius define the following?

Acid

reacts with water to give hydronium ion.

How did Arrhenius define the following?

Base

produces hydroxide ion in water.

Do the following undergo dissociation or ionization in water?

NaOH

H2SO4

HNO3

NH3

Compounds that dissociate must already contain ions, where those that ionize do not already contain ions.

NaOH: dissociation HNO3: ionization

H2SO4: ionization NH3: ionization

(a) Dynamic equilibrium

is used to describe what happens when weak acids or weak bases are added to water.

is a condition where two opposing processes are occurring at the same rate.

(b) What will happen if acetic acid (HC2H3O2) is added to water?

Acetic acid is a weak acid and will not ionize completely.

An equilibrium will form between its molecular form, HC2H3O2, and the ionized form, H+ and C2H3O2-.

Why don't we use double arrows in the equation for the reaction of a strong acid with water?

Because a strong acid is a strong electrolyte and a single reaction arrow shows that the reaction occurs completely in one direction.

Are the following strong or weak acids?

HCN , HNO3 , H2SO3 , HCl , HCHO2 , HNO2

Strong acids will ionize completely in water.

HCN: weak HNO3: strong H2SO3: weak

HCl: strong HCHO2: weak HNO2: weak

Iodine, like chlorine, forms several acids. What are the names of the following?

HIO4 , HIO2 , HI , HIO3 , HIO

HIO4: periodic acid HIO3: iodic acid

HIO2: iodous acid HIO: hypoiodous acid

HI: hydroiodic acid

Which of the following are nonelectrolytes? (Several choices may be correct.)

HC2H3O2 , C12H22O11 , CH3OH , H2SO4

C12H22O11 (sucrose, or table sugar)

CH3OH (methyl alcohol)

How are the formulas of the members of a conjugate acid-base pair related to each other?

They differ by a proton (H+).

Within the pair, how can you tell which is the acid?

The acid has one more hydrogen ion than the base.

What is the strongest acid found in water?

H3O+ is the strongest acid found in water because if a stronger acid is added to the water, it will completely dissociate and protonate the water.

In pure sulfuric acid, H2SO4, what is the strongest acid found?

In pure sulfuric acid H2SO4, the strongest acid found is H3SO4+.

What is the strongest base found in water?

OH- is the strongest base found in water because if a stronger base is added to water, it will completely react to remove a proton from the water molecules.

In an acid base equilibrium, can the stronger acid be on the same side of the arrow as the weaker base? Why or why not.

The stronger acid cannot be on the same side of the arrow as the weaker base because the weaker base is the conjugate base of the stronger acid.

Identify the conjugate acid-base pairs. Select all that apply.

HOCl(aq) + H2O(l) = H3O+(aq) + OCl-(aq)

H2O and H3O+

HOCl and OCl-

Which of the acids is stronger? Select the single best answer.

H3O+

Consider the following: CO32- is a weaker base than hydroxide ion, and HCO3- is a stronger acid than water. In the equation below, would the position of equilibrium lie to the left or to the right?

CO32-(aq) + H2O(l) = HCO3-(aq) + OH-(aq)

The side with the weaker substances is favored.

The left, because the weaker acid and weaker base are favored.

Nitric acid, HNO3, is a very strong acid. It is 100% ionized in water. In the reaction below, would the position of equilibrium lie to the left or to the right? NO3-(aq) + H2O HNO3(aq) + OH-(aq)

To the left, because NO3- is a weak base.

What chemical property determines the strength of an acid?

If the chemical bond between the hydrogen and the molecule is weak, the acid is strong.

What are the two properties that have an effect on the strength of the bond between the molecule and the hydrogen atom.

The bond length between the hydrogen atom and the other atom.

The electronegativity of the atom bound to the hydrogen atom.

Choose the stronger acid:

H2Se

Why is this the stronger acid?

The larger central atom forms a weaker bond with hydrogen.

Which of the following compounds is the stronger base? Explain

NH3 is a stronger base than NCl3. This is due to the difference in the electron withdrawing strength of Cl compared with H.

Cl is more electronegative than H and will withdraw more electron density from the nitrogen than hydrogen.

Thus, the nitrogen atom in NCl3 has a greater positive charge than it does in NH3. The greater positive charge means that is more difficult to add H+ to NCl3 than it is to add H+ to NH3.