Chem/Phys Flashcards
How do enzymes catalyze reactions?
An enzyme’s active site exhibits a specific morphology that allows it to arrange the reactants in the ideal spatial orientation for reaction.
Enzyme’s increase the reaction rate by lowering the activation energy of the reaction and they do this by stabilizing the TRANSITION STATE (not the product or the reactant).
Explain chemical shift and deshielding in Proton NMR.
Atoms with high electronegativity pull electrons toward their nuclei, and therefore away from the other atoms in a shared bond. Thus, a hydrogen bonded to an electronegative atom will experience decreased electron density, or increased deshielding. The atom is said to be deshielded because the decrease in electron density leaves it more exposed to the magnetic field.
How is inertia related to velocity?
Inertia is a measure of an objects resistance to a change in its velocity, generally quantified as its mass. If objects have identical mass they will have identical inertia no matter the velocity.
Velocity does not change an object’s inertia but, does change its momentum.
Henderson-Hasselbalch equation
pH = pKa – log[HA]/[A]
HA = Acid A = Conjugate base
when [HA] = [A], pH = pKa
if [HA] > [A], the pH must be less than the pKa, and if [A] > [HA], the pH must be greater than the pKa.
Should be able to look at this question and deduce the following without any calculation: “There is more conjugate base than acid by TWO factors of 10 (0.5 vs. 0.005), so the pH must be TWO units greater than the pKa.” This trend will continue. If there were more base by THREE factors of 10 (i.e., 1000 times more base), the pH would be THREE units greater than the pKa. If there was more acid than base, the same trend would proceed in the opposite direction. For example, if there were 100 times more acid than base (TWO factors of 10), then the pH would be TWO units less than the pKa.
What is a coordinate covalent bond?
Metal coordination complexes form covalent bonds wherein the ligand acts as a Lewis base (electron donor) and the central metal ion acts as a Lewis acid (electron acceptor).
Ex: the bond that forms between NH3 and BF3 is a coordinate covalent bond
Ex: NH3 can react with Ag+ and can produce Ag(NH3)2 where the coordination number is 2.
How do you calculate standard enthalpy changes?
∆H° = Σ∆H°f(products) - Σ∆H°f(reactants)
If the Ksp of chalcocite (Cu2S) is 5.0 x 10^-29, what is the concentration of Cu in a saturated solution of chalcocite?
The solubility expression for Cu2S is therefore as follows: Ksp = [Cu2+]^2[S2-]. If we use x to represent the moles of copper and sulfur ions formed per mole of chalcocite dissolved, we must use 2x for copper because 2 moles of copper ions will be formed for every one mole of chalcocite that dissociates.
Thus, the equation becomes: Ksp = 5 x 10^-29 = (2x)^2(x) = 4x^3. This can be solved by dividing by 4 to give 1.25 x 10^-29 = x^3, or 12.5 x 10^-30 = x^3. Next, we must take the cube root of each side. The cube root of 12.5 needs to be somewhere between 2 and 3 since 2^3 = 8 and 3^3 = 27, we’ll guess it to be 2.3 since 12.5 is much closer to 8 than it is to 27.
To determine the cube root of 10^-30 we simply divide the exponent 30 by 3 (which is equivalent to multiplying it by 1/3). The answer is therefore approximated to be 2.3 x 10^-10 mol L^-1.
What is the entropy change (∆S°) for the reaction shown below:
2SO2(g) + O2(g) ⇌ 2SO3(g) Keq = 6.9 x 10^24
In the equation, three moles of gaseous reactants are converted into two moles of gaseous products. This means the system is getting more ordered, which is a decrease in entropy.
Therefore, ∆S° is less than zero, because the moles of gaseous products are less than the moles of gaseous reactants.
When Keq < 1 is the reaction spontaneous or non-spontaneous? Why or why not?
Recall that ΔG° = -2.3RTlog [Keq]
{K(forward)/K(reverse)} –> when the forward rate constant is smaller than the reverse rate constant, K < 1.
When K< 1 , ΔG° is positive because the log of any number less than one is negative (i.e., the two negative signs cancel to create a positive sign). A positive ΔG° value indicates a non-spontaneous reaction.
What two variables allow you to calculate the strength of the dipole moment generated in a polar-covalent molecule?
Charge and distance.
The relevant formula for calculating dipole moment is helpful, but not necessary to answer the question: µ = qr where µ is the dipole moment q is the charge r is the distance
The strength of the dipole is a function of both the charge and the distance across which that charge acts.
