CHEM 1C Study Guide - Spring 2018, Comprehensive Midterm Notes - Oxygen, Equilibrium Constant, Rate Equation
CHEM 1C
MIDTERM EXAM
STUDY GUIDE
Fall 2018
➔Reaction rate is the number (mol) of chemical reactions occuring in the system per
reaction volume (L) per time (s)
◆Reaction rate is usually measured in mol/(Lxs)
◆A → B : reaction rate is the number of mol/(Lxs) of A converted into B every
second
◆Rate = -△[A]/△tchange in concentration of A over time period △t
◆Rate = △[B]/△tchange in concentration of B over time period △t
● Because [A] decreases with time, △[A] is negative
➔Average rate: ([A]final - [A]initial) / (tfinal - tinitial)
Example: concentration of O2 decreased from 0.0150 M to 0.0140 M in 3 minutes. Estimate the
average reaction rate
Average rate: –△[O2]/△t= –[O2]final – [O2]initial/ tfinal - tinitial
= –0.0140 M – 0.0150 M180 s
= 5.6 x 10-6 mol/ (Lxs)
➔Reaction rate = moles of reactions per volume (L) per time (s)
◆2 A → B
◆For each mole of the reactions occurred:
● Two moles of A disappeared
● One mole of B was formed
◆To get the reaction rate, the rate of change in [A] and [B] has to be corrected by
the stoichiometric coefficients:
● rate = -(½)( △[A]/△t) rate = △[B]/△t
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➔In general, for reaction: aA + bB → cC + dD , the reaction rate can be calculated from
any of the concentrations:
◆Rate = - (1/a)(△[A]/△t) = -(1/b)(△[B]/△t) = (1/c)(△[C]/△t) = (1/d)(△[D]/△t)
Example: write the rate expression for the following reaction:
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
Rate = - △[CH4]/△t = -(½)△[O2]/△t = △[CO2]/△t = - (½)△[H2O]/△t
➔The rate law expresses the relationship between the reaction rate and the
concentrations of the reactants
➔For the reaction: aA + bB → cC + dD , the rate law has the following form:
◆Rate = k[A]x[B]y
● k is the reaction rate constant units: rate: M/s
● Reaction is the xth order in A k,rate constant: M(1-x-y)/s
● Reaction is the yth order in B
● Reaction is (x + y)th order overall
● The rate law does not include products
Example: what is the overall order of the following reaction, given the rate law?
2 X + 3 Y → 2 Z
Rate = k[X]1[Y]2
1 + 2 = 3, so the overall order is 3rd order
What is the unit constant of k from the previous example? 1/M2s
➔Rate laws are normally determined experimentally
➔Reaction order is usually defined in terms of reactant (not product) concentrations
➔The order of the reaction need not be related to the stoichiometric coefficient of the
reactant in the balanced equation
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Reaction rate is the number (mol) of chemical reactions occuring in the system per reaction volume (l) per time (s) Reaction rate is usually measured in mol/(lxs) A b : reaction rate is the number of mol/(lxs) of a converted into b every second. Rate = - [a]/ t change in concentration of a over time period t. Rate = [b]/ t change in concentration of b over time period t. Because [a] decreases with time, [a] is negative. Average rate: ([a] final - [a] initial ) / (t final - t initial ) Example: concentration of o 2 decreased from 0. 0150 m to 0. 0140 m in 3 minutes. Average rate: [o2]/ t= [o2] final [o2] initial / t final - t initial. Reaction rate = moles of reactions per volume (l) per time (s) For each mole of the reactions occurred:
