<< Chapter < Page Chapter >> Page >

Because there is no change in the total number of molecules in the system during reaction, a change in pressure does not favor either formation or decomposition of gaseous nitrogen monoxide.

Effect of change in temperature on equilibrium

Changing concentration or pressure perturbs an equilibrium because the reaction quotient is shifted away from the equilibrium value. Changing the temperature of a system at equilibrium has a different effect: A change in temperature actually changes the value of the equilibrium constant. However, we can qualitatively predict the effect of the temperature change by treating it as a stress on the system and applying Le Châtelier's principle.

When hydrogen reacts with gaseous iodine, heat is evolved.

H 2 ( g ) + I 2 ( g ) 2 HI ( g ) Δ H = −9.4 kJ ( exothermic )

Because this reaction is exothermic, we can write it with heat as a product.

H 2 ( g ) + I 2 ( g ) 2HI ( g ) + heat

Increasing the temperature of the reaction increases the internal energy of the system. Thus, increasing the temperature has the effect of increasing the amount of one of the products of this reaction. The reaction shifts to the left to relieve the stress, and there is an increase in the concentration of H 2 and I 2 and a reduction in the concentration of HI. Lowering the temperature of this system reduces the amount of energy present, favors the production of heat, and favors the formation of hydrogen iodide.

When we change the temperature of a system at equilibrium, the equilibrium constant for the reaction changes. Lowering the temperature in the HI system increases the equilibrium constant: At the new equilibrium the concentration of HI has increased and the concentrations of H 2 and I 2 decreased. Raising the temperature decreases the value of the equilibrium constant, from 67.5 at 357 °C to 50.0 at 400 °C.

Temperature affects the equilibrium between NO 2 and N 2 O 4 in this reaction

N 2 O 4 ( g ) 2 NO 2 ( g ) Δ H = 57.20 kJ

The positive Δ H value tells us that the reaction is endothermic and could be written

heat + N 2 O 4 ( g ) 2 NO 2 ( g )

At higher temperatures, the gas mixture has a deep brown color, indicative of a significant amount of brown NO 2 molecules. If, however, we put a stress on the system by cooling the mixture (withdrawing energy), the equilibrium shifts to the left to supply some of the energy lost by cooling. The concentration of colorless N 2 O 4 increases, and the concentration of brown NO 2 decreases, causing the brown color to fade.

Catalysts do not affect equilibrium

As we learned during our study of kinetics, a catalyst can speed up the rate of a reaction. Though this increase in reaction rate may cause a system to reach equilibrium more quickly (by speeding up the forward and reverse reactions), a catalyst has no effect on the value of an equilibrium constant nor on equilibrium concentrations.

The interplay of changes in concentration or pressure, temperature, and the lack of an influence of a catalyst on a chemical equilibrium is illustrated in the industrial synthesis of ammonia from nitrogen and hydrogen according to the equation

Questions & Answers

why sometime Pressure,P is refered to force over area?
the first fifty elements
Joy Reply
how to complete and balance ionic equation?
what is molar mass?
Wendy Reply
Molar mass is defined as the mass of a sample of a compound divided by the amount of substance of that sample.
or M=m\n mathematically.
atom is the smallest indivisible part of an element that takes place in chemical reaction
Obinna Reply
An atom is the smallest indivisible part of an element
what is periodic table
wats the chemical equation for aspirin
if pumping machine's can pump water ,why can't it pump fuel
what is chemistry?
Mathias Reply
what is an atom
what is an atom?
is the study of matter and the changes it under goes.
under goes through three state they are solid liquid and gas
in a sturctural way formula for C6H12
sorry ,it's properties and structures
what is C6H12
what is H2so4
Tetraoxosulphate(vi) acid
that's nice guyz
what is the empirical formula for methanedioc acid?
you ppl should talk now
please what is hydroxyl group
Gold Reply
the hydroxyl group is a functional group consisting of a hydrogen atom covalently bonded to an oxygen atom.
Names are of homologous series
Josiah Reply
what's an hydroxyl group?
A hydroxy or hydroxyl group is the entity with the formula OH. It contains oxygen bonded to hydrogen. In organic chemistry, alcohols and carboxylic acids contain hydroxy groups. The anion [OH⁻], called hydroxide, consists of a hydroxyl group. 
what are the steps to follow when writing the condensed formula of elements
Jessicafaith Reply
What is organic chemistry
John Reply
what's organic chemistry?
Mr Reply
why do electrons have no mass
Skynetic Reply
hello there
hi and who say electrons has no mass ? it does have but most at time consider negleable
please what is maa
yeah i will calculate it
Because it's mass it very very small compare with mass of atom
it's simple
consider the rxn of butadiene .Butadiene is prepared by the gas phase catalytic dehydrogenation of 1-butene , at 900K and 1 bar. c4H8 (g)_ C4H6 (g) + H2 (g) (a) In order to suppress side reactions , the butane is diluted with steam before it passes into the reactor.Estimate the conversion
Estimate the conversion of 1-butene for a feed consisting of 10 moles of steam per mole of 1-butene. (b) find the conversion if the inerts were absent and side reactions are ignored .
help me please I have tried
wat is the difference between electrochemical chemical corrosion
please how can i solve this project work..modern aid science process and product
what is the definition of chemistry
Sophia Reply
Sophia pls check on fb u will see transcendence Internationale is a group from here just join over, and ask any question in science from there we here created it
the icon is clear white then writing transcendence Internationale study group
U will see it
for now chemistry is the study of matter and it properties, why and how element combined to form other substances
Chemistry is a group that identifies properties of matter and many more
Wow and chemistry also is the systematic study of nature
chemistry is the study of the structure, properties of matter and the effect of addition or removal of heat from substances.
calculate the relative molecular Mass of the following 1 ZnCl2 2 NaNo3 3 HNO3 4 CaO
Reuben Reply
2) 23+14+(16×3)= 3)1+14+(16×3)= 4) 40+16= 1) Zn+71= that's how they do it but for Zn I don't know its mass number
Reuben u are welcome to join the group transcendence Internationale on fb we created it for science students is a question and answering platform for all science subjects
yeah it's fun
hi guys I'm new here, please I need definition of acid and base
please some one should tell me the meaning of hydro carbon
Practice Key Terms 3

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?