Page 26 - Basic physical chemistry for the atmospheric sciences

1 2 Basic physical chemistry

(c) In one gram -molecular weight of a compound there
must be at least one gram-atomic weight of a given
element, or some integral multiple of this weight . Does
this suggest a method for determining atomic weights?
(d) The number of moles in any gas sample can be found by
comparing its volume at STP with 22.4 L.
(e) If two elements form more than one compound, then the
different masses of one that combine with the same mass
of the other are in the ratio of small whole numbers (the
law o f multiple proportions).
(f) A chemical reaction generally starts off fast, slows with
time, and finally ceases.
(g) The equilibrium constant for a chemical reaction is inde­
pendent of the exact mechanism of the reaction, the rate
at which the equilibrium is approached , or the direction
from which the equilibrium is approached . (Compare
with a mechanical system.)
(h) Only for reactions in which the number of molecules
of gaseous reactants is d i fferent from the number of
molecules of gaseous products does a volume change
remove the system from equilibrium.
1.8. Write expressions for the equilibrium constants (Kc) for
both the forward and reverse reactions of the following
chemical equations:
(a) N2(g)+3H2(g)�2NHJ(g)
(b) N20(g)+!Oz(g)�2NO(g)
(c) 4NH3(g)+302(g)�2N2(g)+6H20(g)
(d) NH4Cl(s)�NH3(g) + HCl(g)
1 . 9. If the equilibrium constant (Kc) for the reaction
A(g) + 2B(g)�G(g) + 3H(g)

(where A , B , G, and H represent any chemical species) is
3
2. I 1 0 - , what concentration of H(g) will be in equilibrium
x
with O. I M of A(g), 0.25 M of B(g), and 0.02 M of G(g)?
I. I 0. The equilibrium constant (K ) for the reaction
P
2S02(g) + Oz(g) � 2S03(g)

at 727°C is 3.39. What is the partial pressure of SOig) that
would be in equilibrium with 0 . 2 0 atm of SOz(g) and 0.80
atm of Oz(g)?