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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

how does Neisseria cause meningitis
Nyibol Reply
what is microbiologist
Muhammad Reply
what is errata
Muhammad
is the branch of biology that deals with the study of microorganisms.
Ntefuni Reply
What is microbiology
Mercy Reply
studies of microbes
Louisiaste
when we takee the specimen which lumbar,spin,
Ziyad Reply
How bacteria create energy to survive?
Muhamad Reply
Bacteria doesn't produce energy they are dependent upon their substrate in case of lack of nutrients they are able to make spores which helps them to sustain in harsh environments
_Adnan
But not all bacteria make spores, l mean Eukaryotic cells have Mitochondria which acts as powerhouse for them, since bacteria don't have it, what is the substitution for it?
Muhamad
they make spores
Louisiaste
what is sporadic nd endemic, epidemic
Aminu Reply
the significance of food webs for disease transmission
Abreham
food webs brings about an infection as an individual depends on number of diseased foods or carriers dully.
Mark
explain assimilatory nitrate reduction
Esinniobiwa Reply
Assimilatory nitrate reduction is a process that occurs in some microorganisms, such as bacteria and archaea, in which nitrate (NO3-) is reduced to nitrite (NO2-), and then further reduced to ammonia (NH3).
Elkana
This process is called assimilatory nitrate reduction because the nitrogen that is produced is incorporated in the cells of microorganisms where it can be used in the synthesis of amino acids and other nitrogen products
Elkana
Examples of thermophilic organisms
Shu Reply
Give Examples of thermophilic organisms
Shu
advantages of normal Flora to the host
Micheal Reply
Prevent foreign microbes to the host
Abubakar
they provide healthier benefits to their hosts
ayesha
They are friends to host only when Host immune system is strong and become enemies when the host immune system is weakened . very bad relationship!
Mark
what is cell
faisal Reply
cell is the smallest unit of life
Fauziya
cell is the smallest unit of life
Akanni
ok
Innocent
cell is the structural and functional unit of life
Hasan
is the fundamental units of Life
Musa
what are emergency diseases
Micheal Reply
There are nothing like emergency disease but there are some common medical emergency which can occur simultaneously like Bleeding,heart attack,Breathing difficulties,severe pain heart stock.Hope you will get my point .Have a nice day ❣️
_Adnan
define infection ,prevention and control
Innocent
I think infection prevention and control is the avoidance of all things we do that gives out break of infections and promotion of health practices that promote life
Lubega
Heyy Lubega hussein where are u from?
_Adnan
en français
Adama
which site have a normal flora
ESTHER Reply
Many sites of the body have it Skin Nasal cavity Oral cavity Gastro intestinal tract
Safaa
skin
Asiina
skin,Oral,Nasal,GIt
Sadik
How can Commensal can Bacteria change into pathogen?
Sadik
How can Commensal Bacteria change into pathogen?
Sadik
all
Tesfaye
by fussion
Asiina
what are the advantages of normal Flora to the host
Micheal
what are the ways of control and prevention of nosocomial infection in the hospital
Micheal
what is inflammation
Shelly Reply
part of a tissue or an organ being wounded or bruised.
Wilfred
what term is used to name and classify microorganisms?
Micheal Reply
Binomial nomenclature
adeolu
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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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