EjerciciosFyQ

Calculation of equilibrium constants and degree of dissociation of N2O4 (8413)

F_y_Q — 2025-03-14T05:49:47Z

At and 1 atm, dissociates into by according to the following equilibrium:

2NO2(g)}" title="\ce{N2O4(g) <=> 2NO2(g)}" />

Calculate:

a) The values of the equilibrium constants and at this temperature.

b) The percentage of dissociation at and a total pressure of 0.1 atm.

Data: .

The first step is to determine the number of moles of each substance at equilibrium, based on the initial moles and the degree of dissociation ():

\underset{2n_0\alpha}{\ce{2NO2(g)}}}" title="\ce{\underset{n_0(1-\alpha)}{\ce{N2O4(g)}}} \ce{<=> \underset{2n_0\alpha}{\ce{2NO2(g)}}}" />

Since the degree of dissociation is , the moles can be written as:

\underset{0.4n_0}{\ce{2NO2(g)}}}" title="\ce{\underset{0.8n_0}{\ce{N2O4(g)}}} \ce{<=> \underset{0.4n_0}{\ce{2NO2(g)}}}" />

The total number of moles at equilibrium is the sum of all species:

Next, calculate the mole fraction for each substance:

a) The equilibrium constant in terms of partial pressures is:

Substitute the values into this equation to determine the constant:

The equilibrium constant in terms of concentrations is calculated as:

The change in the number of moles of gas is one, so substitute the values to find the constant:

b) When the total pressure of the system changes to 0.1 amt, the equilibrium shifts to favor greater dissociation of . The same expression for holds, and it is used to calculate the new degree of dissociation under these conditions. Be cautious to express the mole fractions in terms of the initial moles:

For simplicity, work with the denominator and substitute to make solving easier:

pH and pOH of an acetic acid solution (8401)

F_y_Q — 2025-02-17T05:12:03Z

Calculate the pH and pOH of a 0.001 mol/L acetic acid solution, given its ionization constant

From the ionization constant value, you can calculate the concentration of ions at equilibrium:

CH3COO^- + H3O^+}}}" title="\color[RGB]{2,112,20}{\textbf{\ce{CH3COOH + H2O <=> CH3COO^- + H3O^+}}}" />

The acidity constant follows the equation:

The equilibrium concentrations, based on the initial concentration, are as follows:

Substitute these concentrations into the equilibrium constant equation to get:

You can do one of two things: solve the quadratic equation or assume that, given the small value of the constant, the denominator is very close to one. Here's how to do each.

Solving the quadratic equation:

You get the value . The other value obtained is negative and lacks chemical significance.

Approximating the denominator as one:

Since the acid concentration is low, it's not a good idea to use the approximation, and it is preferable to solve the quadratic equation to avoid an error of over .

Taking the first calculated dissociation degree value, you can calculate the equilibrium hydronium concentration:

The pH calculation is straightforward:

You can calculate the pOH considering their relationship:

Relationship between molarity and normality (8380)

F_y_Q — 2025-01-27T04:52:56Z

Calculate the normality of the following solutions: a) (2 M) b) (0.4 M) c) (3 M) d) (1 M) e) (2 M)

Normality is defined as the number of equivalents of solute in one liter of solution. The mass of an equivalent is the molecular mass divided by the number of "H" or "OH" groups in the acid or base considered. This means that the relationship between normality and molarity is that normality is equal to molarity multiplied by the number of "H" or "OH" groups in the species.

a)

b)

c)

d)

e) (because it is a salt with a 1:1 stoichiometry between its ions).

General gas law (8316)

F_y_Q — 2024-09-17T02:52:07Z

Calculate the final temperature of a gas enclosed in a volume of 2 L at 1 atm, if we reduce its volume to 0.5 L and its pressure increases to 3.8 atm.

You will use the state equation of gases:

Solving for the value of :

True or false about atoms (8309)

F_y_Q — 2024-09-14T03:29:36Z

Decide whether the following statements are true or false. Explain the reason if you find them false:

a) An atom is different from an ion.

b) Atoms have more electrons than protons.

c) Two cations attract each other only if they are in contact.

d) Carbon atoms can be better conductors than potassium atoms.

a) TRUE.

b) FALSE. Atoms are neutral species, unlike ions, so they must have the same number of protons as electrons.

c) FALSE. They do not attract in any case because they are particles with the same charge, so they repel each other instead of attracting.

d) FALSE. Potassium is a metal and therefore has higher electrical conductivity than carbon, which is a non-metal. The allotropic form of carbon called graphite is conductive, but its conductivity is about ten times lower than that of potassium, making it a worse conductor.

Application of Graham's law: hydrogen diffusion rate (8308)

F_y_Q — 2024-09-12T04:06:10Z

Determine the diffusion rate of hydrogen, knowing that the diffusion rate of oxygen is 2 minutes.

Graham's law relates the diffusion rates of two gases to their molecular masses. If the gases are A and B, the relationship is:

For hydrogen and oxygen, both being diatomic, the molecular masses are:

The relationship between their diffusion rates will be:

This means hydrogen diffuses four times faster than oxygen, so the diffusion rate of hydrogen will be 0.5 minutes, or 30 seconds.

Molarity from % (m/V) concentration (8303)

F_y_Q — 2024-09-08T03:42:27Z

Calculate the molarity of a sulfurous acid solution whose concentration is (m/V).

First, set a quantity of solution as the basis for calculation. Consider 100 mL of solution, which gives you 8 g of solute, , (these amounts are the “translation” of m/V).

The moles corresponding to that mass of solute are obtained from the molecular mass of the acid:

Calculate the moles equivalent to the mass of solute:

The molarity is the ratio between the moles of solute and the volume of the solution, expressed in liters, i.e., 0.1 L (because you considered 100 mL at the beginning):

Molar fraction and molality of a solution (8298)

F_y_Q — 2024-09-03T07:07:35Z

A solution contains by mass of HCl:

a) Calculate the molar fraction of HCl.

b) Calculate the molality of HCl in the solution.

You can fix an amount of 100 g of solution to solve the problem because, in those 100 g of solution, there will be 36 g of HCl (which is what the percentage means) and 64 g of water. Convert both quantities to moles:

a) Calculate the molar fraction:

b) Calculate the molality. This is defined as the ratio between the moles of solute and the mass of solvent, expressed in kilograms:

Calorimetry: final temperature of a mixture (8297)

F_y_Q — 2024-09-02T03:37:09Z

100 g of water at is mixed with 300 g of water at . What will be the final temperature of the mixture?

The heat lost by the hot water is equal to the heat gained by the cold water.

For the hot water:

For the cold water:

The heat lost is considered negative, and the heat gained is positive:

Equating the heat exchanges:

Eliminating the specific heat of water from the equation and simplifying:

Solving for the final temperature:

Gibbs free energy and spontaneity (8296)

F_y_Q — 2024-08-29T18:59:47Z

The standard enthalpy of reaction between methane and dichlorine to produce chloromethane and hydrogen chloride is . Knowing the standard entropy change is , calculate the standard Gibbs free energy change at a given temperature, and determine if the process is spontaneous under these conditions.

The reaction to be studied is:

CH3Cl(g) + HCl(g)}}}" title="\color[RGB]{2,112,20}{\textbf{\ce{CH4(g) + Cl2(g) -> CH3Cl(g) + HCl(g)}}}" />

The expression to calculate the Gibbs free energy is:

Simply substitute the values provided in the statement, considering that the enthalpy is given in kJ, and perform the calculation: