<span>Yes its H2O , the H2O and the OH- are acid/Base Conjugate pair................just like NH3 and NH4
</span>
18. <span>Answer is </span>
A<span>
<span>Since the enthalpy of reaction is positive, the
forward reaction is<span> an endothermic reaction which means the energy
is gained from the surrounding to happen the reaction. If the temperature
decreases, according to the </span></span>Le Chatelier's principle, the system tries to become equilibrium
by increasing temperature. Since forward reaction is endothermic (because of
the bond breaking), the backward reaction is exothermic (because of the bond
making) which releases the energy to the surroundings. This makes the increase
of temperature. So if the backward reaction is promoted because of the decrease
of temperature, then the concentration of H</span><span>₂ will decrease.</span>
<span>
</span>
19. Answer is A.
The reactant side
has 2 moles/molecules of reactants and the product side has 4 moles/molecules
of products which come from 1 N₂(g) and 3 H₂<span>(g). If the pressure is reduced in the system, according to the Le Chatelier's principle, the
system tries to increase the pressure. </span><span>Hence, forward
reaction is promoted because of the higher number
of molecules in product side. If the forward reaction is promoted, the
concentration of NH</span>₃(g) will decreased.
<span>20. </span>Answer is C.
If the concentration
of reactant is increased in the
system, according to the Le Chatelier's principle, the system tries
to reduce the concentration of that reactant. So if NH₃(g) concentration
is increased, then to be equilibrium, the forward reaction will be promoted.
Then the concentration of N₂<span>(g) will increase.</span>
<span> </span>
For this question, I think it is the other way around. It is true that chloroacetic acid is stronger in strength than acetic acid. Acid strength is measured as the equilibrium constant of the reaction <span>HA -----> H+ + A-
</span><span> In acetic acid, the anion produced by dissociation is CH3-COO-; in chloroacetic acid it is CH2Cl-COO-. Comparing the two, in the first one the negative charge is taken up mostly by the two oxygen atoms. In the second there is also an electronegative chlorine atom nearby to draw more charge towards itself. Therefore, the charge is less concentrated in the chloroacetate ion than it is in the acetate ion, and, accordingly, chloroacetic acid is stronger than acetic acid. </span>
It would be C!!!!!!!!!!!!!
