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Measuring rates of reaction

How the rate of a reaction is measured will depend on what the reaction is, and what product forms. Look back to the reactions that have been discussed so far. In each case, how was the rate of the reaction measured? The following examples will give you some ideas about other ways to measure the rate of a reaction:

  • Reactions that produce hydrogen gas: When a metal dissolves in an acid, hydrogen gas is produced. A lit splint can be used to test for hydrogen. The 'pop' sound shows that hydrogen is present. For example, magnesium reacts with sulfuric acid to produce magnesium sulphate and hydrogen. M g ( s ) + H 2 S O 4 M g S O 4 + H 2
  • Reactions that produce carbon dioxide: When a carbonate dissolves in an acid, carbon dioxide gas is produced. When carbon dioxide is passes through limewater, it turns the limewater milky. This is a simple test for the presence of carbon dioxide. For example, calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide. C a C O 3 ( s ) + 2 H C l ( a q ) C a C l 2 ( a q ) + H 2 O ( l ) + C O 2 ( g )
  • Reactions that produce gases such as oxygen or carbon dioxide: Hydrogen peroxide decomposes to produce oxygen. The volume of oxygen produced can be measured using the gas syringe method ( [link] ). The gas collects in the syringe, pushing out against the plunger. The volume of gas that has been produced can be read from the markings on the syringe. For example, hydrogen peroxide decomposes in the presence of a manganese(IV) oxide catalyst to produce oxygen and water. 2 H 2 O 2 ( a q ) 2 H 2 O ( l ) + O 2 ( g )
    Gas Syringe Method
  • Precipitate reactions: In reactions where a precipitate is formed, the amount of precipitate formed in a period of time can be used as a measure of the reaction rate. For example, when sodium thiosulphate reacts with an acid, a yellow precipitate of sulfur is formed. The reaction is as follows: N a 2 S 2 O 3 ( a q ) + 2 H C l ( a q ) 2 N a C l ( a q ) + S O 2 ( a q ) + H 2 O ( l ) + S ( s ) One way to estimate the rate of this reaction is to carry out the investigation in a conical flask and to place a piece of paper with a black cross underneath the bottom of the flask. At the beginning of the reaction, the cross will be clearly visible when you look into the flask ( [link] ). However, as the reaction progresses and more precipitate is formed, the cross will gradually become less clear and will eventually disappear altogether. Noting the time that it takes for this to happen will give an idea of the reaction rate. Note that it is not possible to collect the SO 2 gas that is produced in the reaction, because it is very soluble in water.
    At the beginning of the reaction beteen sodium thiosulphate and hydrochloric acid, when no precipitate has been formed, the cross at the bottom of the conical flask can be clearly seen.
  • Changes in mass: The rate of a reaction that produces a gas can also be measured by calculating the mass loss as the gas is formed and escapes from the reaction flask. This method can be used for reactions that produce carbon dioxide or oxygen, but are not very accurate for reactions that give off hydrogen because the mass is too low for accuracy. Measuring changes in mass may also be suitable for other types of reactions.

Questions & Answers

what does the word emitted mean?
Mwinga Reply
to be ejected or released
Khathutshelo
Ok thanks
Mwinga
what are the hooke laws
Tyriek Reply
what do really asked in exam
Leiyo Reply
hi please help me how to balance redox reactions?
Brian Reply
Which equation do u wanna balance
Rifumo
i tried to write it but my phone just can't write it Cr2 O72-(aq) + H2S (aq) Cr3 (aq) + S(s)
Brian
show is the equation
Pride
us
Pride
hello. what is the difference between a primary, secondary and tertiary alcohol
Thokozani Reply
primary the C=bonded to 1 Carbon atom.... secondary=bonded to 2 carbon atoms tertiary=bonded to 3 carbon atoms
Christina
I hope you're answered
Christina
thanks Christina
Baningi
My pleasure
Christina
Thank you Christina. This is very helpful 😀👍👍💯
Thokozani
💯💯
Thokozani
Anytime Thokozani
Christina
How to calculate pH?
Thabo
thank you guys i didn't know about the primary, secondary and tertiary alcohols
Brian
thank you Christina
Brian
Hey guys which topic does AC nd DC generator falls
Phumelele
electrodynamics
Christina
thank you
Phumelele
can somebody help me with functional isomers
Baningi Reply
function isomer has the same molecular formula but different functional group
Thokozani
what's momentum
Luvelo Reply
the product of an objects mass times velocity. it is mainly prevalent in collisions.
tyrique
momentum
Sesethu
in order to produce an interference pattern, the waves used must be what?
Methane contains C and H. This compound is
Juan Reply
ketones's functional group
Moloi Reply
Why does the carboxyl group have acidc properties?
Evi Reply
carboxylic acids
tyrique
Besides improving appearance what is another reason why medal is electro plated
Elizabeth Reply
it is made of metal
Reunity
thanks
Elizabeth
what is different between Dependent variable and independent variables
Elizabeth
difference between A.c and D.c
Gerrard
AC has slip rings DC has split rings commutator
Mohludi
to avoid rust and to improve strength and conductivity
Shubham
the variable whose value doesn't depend on other is known as independent variable ex time
Shubham
are UV rays dangerous?
Khathutshelo Reply
no
Lianda
what's this?
Lianda
if there is extensive exposure, it can lead to skin cancer
tyrique
yes depend upon their intensity
Shubham
i hv a problem with this chapter because i also have problem with Newton's laws of motion
Kearabetswe Reply
I have a problem with calculation in Newton's law of motion
Vuyokazi
me also VuyokAzi
Amahle
what's the question
Christina
Which area in particular?
Kevo
just get the hang if free body diagrams,know the directions.
Muregu
I know how to draw free diagram I have a problem with calculation in second law
Vuyokazi
what is the wave model of atom ?
Trazy Reply
guys what is momentum
Luvelo
@Luvelo... Momentum is the product of an object's mass and its velocity.
Christina
the model based on wave nature of electron
Shubham
Can you state the Doppler effect in words
Nombuyiselo Reply
State Coulomb's law in words
Nombuyiselo
the magnitude of the electrostatic force exerted point on each other is directly proportional to the product on magnitude of charges and inversely proportional to the square distance between them
Cassiey
the change in frequency of the sound detected by a listener because sound source and listener have different velocity
Elizabeth

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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