V = nRT; or, dividing both sides by V, = MRT, where M = molarity.
Example: What are the osmotic pressures of 1.00 M sugar and 1 M aluminum chloride solutions at 25°C?
sugar= MRT = (1 mol/L)(0.0821 L*atm/mol*K)(298 K) = 24.5 atm
AlCl3= MRT = (1 mol/L)(4 mol ion/mol)(0.0821 L*atm/mol*K)(298 K) = 97.9 atm
Colloids are defined by particle size = 1.0 nm< colloid < 100 nm (particles in solution are 0.1 - 1.0 nm in diameter, whereas particles > 100 nm dispersed in a fluid are considered to be in suspension.) Colloids generally do not settle out.
Study of rates and mechanisms of reactions. Experimentally, look at rates of reactions, use this information to guess mechanisms
Concentrations are assumed to be in Molarity unless otherwise specified.
Consider the reaction:
r [A] [B]2 [C]0,or
r = k [A] [B]2
This expression is referred to as a Rate Lawwith the sum of various exponents referred to as the order of the reaction. The overall order of this reaction is thus 3rd order - it is first order in A, second order in B, and zero order in C.
Looking at the different reaction orders:
- First Order: For A C, or A + B C + D, etc.
- r = k [A]; & r =-d [A]/dt = d[C]/dt.
- Note that we could measure the rate by measuring the changes in concentrations of any of the species. That is, even though changing [B] won't affect the rate, we could measure the rate change occurring by changing [A] by measuring [B] since the stoichiometry says that for each A lost, one B is also lost!
- Note: if double [A], double rate; triple [A], triple rate.
- Second order: For A C, or A + B C + D, etc. Two cases:
r = k [A][B]
- Note if double [A] or [B] will double rate; if double both [A] and [B] will quadruple rate
r = k [A]2, etc.
- Note if double [A] will quadruple rate, if triple [A] will increase rate nine-fold
- Higher order reactions occur, but are uncommon.
- Zero order: r = k[A]0 = k: Only occurs with catalysts, important in enzyme catalysis. 0 order also only occurs above a minimum [A].
The experiment is to increase the concentration of a single reactant, and observe the rate. Sometimes the order will be obvious (i.e. double, double = directly proportional = 1st order). If not, then can take the results of two experiments and divide them and do some algebraic manipulations to find the correct order.
Example: Find the order of the reaction given the data below.
|1||0.0167||3.61 x 10-3|
|2||0.0569||4.20 x 10-2|
r = k [A]n
r1/r2 = (k [A]1n)/(k [A]2n)
r1/r2 = ([A]1/[A]2)n
But we want to find n, so take logs of both sides:
ln (r1/r2) = ln ([A]1/[A]2)n = n ln ([A]1/[A]2)
n = ln (r1/r2)/ln ([A]1/[A]2)
n = ln(0.0361 / 0.420)/ln(0.0167 / 0.0569)) = 2
|Syllabus / Schedule|
© R A Paselk
Last modified 18 April 2011