<< Chapter < Page Chapter >> Page >

Determining relative changes in concentration

Complete the changes in concentrations for each of the following reactions.

(a) C 2 H 2 ( g ) + 2 Br 2 ( g ) C 2 H 2 Br 4 ( g ) x _____ _____

(b) I 2 ( a q ) + I ( a q ) I 3 ( a q ) _____ _____ x

(c) C 3 H 8 ( g ) + 5 O 2 ( g ) 3 CO 2 ( g ) + 4 H 2 O ( g ) x _____ _____ _____

Solution

(a) C 2 H 2 ( g ) + 2 Br 2 ( g ) C 2 H 2 Br 4 ( g ) x 2 x x

(b) I 2 ( a q ) + I ( a q ) I 3 ( a q ) x x x

(c) C 3 H 8 ( g ) + 5 O 2 ( g ) 3 CO 2 ( g ) + 4 H 2 O ( g ) x 5 x −3 x −4 x

Check your learning

Complete the changes in concentrations for each of the following reactions:

(a) 2 SO 2 ( g ) + O 2 ( g ) 2 SO 3 ( g ) _____ x _____

(b) C 4 H 8 ( g ) 2 C 2 H 4 ( g ) _____ −2 x

(c) 4 NH 3 ( g ) + 7 H 2 O ( g ) 4 NO 2 ( g ) + 6 H 2 O ( g ) _____ _____ _____ _____

Answer:

(a) 2 x , x , −2 x; (b) x , −2 x; (c) 4 x , 7 x , −4 x , −6 x or −4 x , −7 x , 4 x , 6 x

Got questions? Get instant answers now!

Calculations involving equilibrium concentrations

Because the value of the reaction quotient of any reaction at equilibrium is equal to its equilibrium constant, we can use the mathematical expression for Q c (i.e., the law of mass action ) to determine a number of quantities associated with a reaction at equilibrium. It may help if we keep in mind that Q c = K c (at equilibrium) in all of these situations and that there are only three basic types of calculations:

  1. Calculation of an equilibrium constant . If concentrations of reactants and products at equilibrium are known, the value of the equilibrium constant for the reaction can be calculated.
  2. Calculation of missing equilibrium concentrations . If the value of the equilibrium constant and all of the equilibrium concentrations, except one, are known, the remaining concentration can be calculated.
  3. Calculation of equilibrium concentrations from initial concentrations . If the value of the equilibrium constant and a set of concentrations of reactants and products that are not at equilibrium are known, the concentrations at equilibrium can be calculated.

A similar list could be generated using Q P , K P , and partial pressure. We will look at solving each of these cases in sequence.

Calculation of an equilibrium constant

Since the law of mass action is the only equation we have to describe the relationship between K c and the concentrations of reactants and products, any problem that requires us to solve for K c must provide enough information to determine the reactant and product concentrations at equilibrium. Armed with the concentrations, we can solve the equation for K c , as it will be the only unknown.

[link] showed us how to determine the equilibrium constant of a reaction if we know the concentrations of reactants and products at equilibrium. The following example shows how to use the stoichiometry of the reaction and a combination of initial concentrations and equilibrium concentrations to determine an equilibrium constant. This technique, commonly called an ICE chart—for I nitial, C hange, and E quilibrium–will be helpful in solving many equilibrium problems. A chart is generated beginning with the equilibrium reaction in question. Underneath the reaction the initial concentrations of the reactants and products are listed—these conditions are usually provided in the problem and we consider no shift toward equilibrium to have happened. The next row of data is the change that occurs as the system shifts toward equilibrium—do not forget to consider the reaction stoichiometry as described in a previous section of this chapter. The last row contains the concentrations once equilibrium has been reached.

Questions & Answers

What is greatest modification made in dalton's atomic theory?
Ngwesse Reply
Types of electrolytes
Treasure Reply
Strong, weak and non-electrolytes
Grace
hello
Alieu
hi
Michelle
Hi
Esho
how are you doing dear?
Alieu
hello guys I'm new here
Nnamdi
I'm new too
Michelle
welcome
Alieu
thanks what's this platform all about
Nnamdi
list 6 subatomic particles and their mass, speed and charges
Dubem Reply
combination of acid and base
Ayibiro Reply
that salt
Talhatu
calculate the mass in gram of NaOH present in 250cm3 of 0.1mol/dm3 of its solution
Omego Reply
The mass is 1.0grams. First you multiply the molecular weight and molarity which is 39.997g/mol x 0.1mol/dm3= 3.9997g/dm3. Then you convert dm3 to cm3. 1dm3 =1000cm3. In this case you would divide 3.9997 by 1000 which would give you 3.9997*10^-3 g/cm3. To get the mass you multiply 3.9997*10^-3 and
Kokana
250cm3 and get the mass as .999925, with significant figures the answer is 1.0 grams
Kokana
nitrogen, phosphorus, arsenic, antimony and Bismuth
faith Reply
What is d electronic configuration of for group 5
Miracle Reply
Can I know d electronic configuration of for group 5 elements
Miracle
2:5, 2:8:5, 2:8:8:5,...
Maxime
Thanks
Miracle
Pls what are d names of elements found in group 5
Miracle
define define. define
Muh Reply
what is enthalpy
Ayilaran Reply
total heat contents of the system is called enthalpy, it is state function.
Sajid
background of chemistry
Banji Reply
what is the hybridisation of carbon in formic acid?
Maham Reply
sp2 hybridization
Johnson
what is the first element
Josh Reply
HYDROGEN
Liklai
Element that has positive charge and its non metal Name the element
Liklai
helium
oga
sulphur
oga
hydrogen
Banji
account for the properties of organic compounds
mercy Reply
properties of organic compounds
mercy
what's the difference between molecules and compounds
Amha Reply
A compound can be a molecule however compounds must contain more than one element. For example ozone, O3 is a molecule but not a compound.
Justin
what is che? nd what is mistry?
Mukhtar
What's elixir?
EMEKA Reply
An Elixir is a substance held capable of changing base metals into Gold.
Nwafor

Get the best Chemistry course in your pocket!





Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Chemistry' conversation and receive update notifications?

Ask