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Chemical change

Physical and chemical change

This section starts by distinguishing between physical and chemical changes of matter. Matter does not change during a physical change, it is the arrangement of molecules that change. Matter changes during chemical changes through decomposition and syntheses reactions. Physical and chemical changes are compared with respect to the arrangement of particles, conservation of mass, energy changes and reversibility. The role of intermolecular forces during phase changes (a physical change) is highlighted. Understanding of concepts is enhanced by examples which include diagrams, experiments and investigations.

Representing chemical change

As a Physical Sciences educator you will welcome this section as it will bridge the gap learners might have in conceptual understanding and skills to represent chemical change. The content revised includes: common chemical symbols, writing chemical formulae and balancing chemical equations by applying the law of conservation of mass. The four labels used to represent the state (phase) of compounds in the chemical equation are:

  • (g) for gaseous compounds
  • (l) for liquids
  • (s) for solid compounds and
  • (aq) for an aqueous (water) solution

Learners will develop the skills to balance chemical equations when they study and apply the steps discussed in the text. Learners need to do the proposed investigation and work through the examples and exercises to assess understanding and consolidate learning.

Reactions in aqueous solutions

Many reactions in chemistry and all reactions in living systems take place in water (or aqueous solutions). In almost all these reactions ions are present. We explore:

  • ions in aqueous solutions;
  • electrical conductivity; and
  • the three main types of reactions that occur in aqueous solutions, namely precipitation, acid-base and redox reactions.

Ions in aqueous solutions

Learners need to understand why water is a polar molecule, to apply their knowledge in further discussions. It is this unique property that allows ionic compounds to dissolve in water. In plants and animals water is the carrier of these dissolved substances making life possible. The process of dissociation is thoroughly explained using words, a definition, image and an equation. The equation for the dissolution of sodium chloride is:

NaCl ( s ) Na + ( aq ) + Cl ( aq ) NaCl(s)→Na^{{}+{}}(aq) + Cl^{{}-{}}(aq)

Electrolytes, ionisation and conductivity

Concepts are explored using: definitions, equations and experiments.

  • Conductivity is a measure of the ability of water to conduct an electric current. The more ions in the solution, the higher its conductivity.
  • An electrolyte is a material that increases the conductivity of water when dissolved in it. Electrolytes are divided into strong and weak electrolytes.
  • A non-electrolyte is a material that does not increase the conductivity of water when dissolved in it. The substance that goes into a solution becomes surrounded by water molecules separate from each other, but no chemical bonds are broken. This is a physical change. In the oxygen the reaction is reversible because oxygen is only partially soluble in water and comes out of solution very easily.

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Purification of water by natural plants and wetlands
Gift Reply

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Source:  OpenStax, Physical science grade 10 teachers' guide - siyavula webbook. OpenStax CNX. Aug 10, 2011 Download for free at http://cnx.org/content/col11342/1.1
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