Physical Chemistry Answers

Is activation energy is temperature independent?

Which of the following statement about enthalpy is incorrect
A. Enthalpy and internal energy of a system are always identical
B. Enthalpy is a state of function
C. $\Delta H$ is the enthalpy change at constant pressure
D. $\Delta H$ is the enthalpy change at constant pressure
Reactions which absorb heat have a positive DH

If temperature and volume are same, the pressure of gas obeying van der Waals equation is smaller than that of an ideal gas" . What is the explanation behind this?

Water occurs in different states: Ice, liquid, vapor and as supercritical fluid. To reach the supercritical state, water has to go through the so-called "supercritical point". At this point:
options:
the compressibility of liquid and vapor phase are equal.


there is no longer any interaction between single water molecules.


ice, liquid and vapor phase are co-existing.


water loses its polar moment and becomes a non-polar solvent.

When using an independent particle model, an MO ψ is expressed in LCAO form, i.e. as a linear combination of atomic orbitals {ϕ_1, ϕ_2, . . . , ϕ_K}, (1)
and the expansion coefficients are determined from secular equation: the Hamiltonian is the one electron operator h and the “orbital energy” ε. Find the MOs and orbital energies for a linear
polyene (Cn Hn+2), taking ϕ_µ to be 2p_z AOs on C and including only nearest-neighbor matrix
element, with
(ϕ_µ|h|ϕ_µ) = α, (ϕ_µ|h|ϕ_µ±1) = β (2)
and with the neglect of the overlap.
Give explicitly the MOs and orbital energies for N = 3 and N = 4.

Write the approximate net reaction between carbonate ion and water in a system that is exposed to atmospheric carbon dioxide. Is the resulting water mildly acidic or mildly alkaline? Explain why the production of bicarbonate ion from carbonate ion does not inhibit its production from carbon dioxide, and vice-versa.

Write the approximate net reaction between carbonate ion and water in a system that is not also exposed to atmospheric carbon dioxide. Is the resulting water acidic, alkaline, or neutral?

The bicarbonate ion, HCO3-- can potentially act as an acid or as a base in water. Write the chemical equations for these two processes, and from the information given in Manahan, determine the corresponding acid and base dissociation constants. Given the relative magnitudes of the dissociation constants, decide whether the dominant reaction of bicarbonate in water will be as an acid or as a base. Calculate the pH of an aqueous 0.010 M solution of sodium bicarbonate in water using the dominant reaction alone, and assuming that the amounts of carbonate ion and carbonic acid from other sources are negligible in this case.

The total alkalinity of a natural water sample is measured by titration and found to contain 1.5 x 10-3 alkalinity equivalents (total alkalinity = [HCO3-] + 2[CO32-] + [OH-] - [H+1]). The pH of this water sample is 10.40. Use this information to calculate answers to the following questions. Use the equations given below.
a. What percent of the carbonate present is in the form of the carbonate ion (CO32-) at pH = 10.40?
b. What is the molar concentration of carbonate ion (CO32-) in this sample?
c. What would be the concentration of calcium ion if this sample is in equilibrium with solid calcium carbonate.

Which of the following statements about enthalpy is incorrect?