# CHEM 1C Study Guide - Comprehensive Final Exam Guide - Oxygen, Equilibrium Constant, Rate Equation

86 views46 pages

CHEM 1C

➔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

find more resources at oneclass.com

find more resources at oneclass.com

➔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: