| |
|
|
| |
 |
| Summary
|
|
- Some high fat foods such as potato chips are packaged
in materials that protect them from light and oxygen and the containers are
flooded with nitrogen to further exclude oxygen
- At times, to avoid
the presence of oxygen altogether, vacuum packaging is used in some
processed foodstuff
- In a physical change the shape, size, appearance or state of a substance may alter, but it is a temporary change, which is usually reversible. No new substance
is formed, hence no change in the mass of the substance and no energy changes are involved.
- In a chemical change, new substances are formed and energy changes are involved. There is a change in mass during the reaction and a permanent change takes place.
- The chemical formula of a substance is the symbolic representation of
the actual number of atoms present in one molecule of that substance
- A complete chemical equation represents the reactants, products and their physical states symbolically and is a balanced account of a chemical transaction.
- A chemical equation is balanced so that the numbers of atoms of each
type involved in a chemical reaction are the same on the reactant and
product sides of the equation
- Equations must always be balanced.
Equations are balanced by the hit and trial method.
- The rate of a
chemical reaction depends on temperature (heat), presence of light, presence
of catalyst, application of pressure and the passage of electric current
-
Chemical reactions that proceed with evolution of heat energy, that is, in
which heat is given out along with the product, are called exothermic
reactions
- Chemical reactions that proceed with the absorption of
heat energy are called endothermic reactions
- Combination or
synthesis is a reaction in which a new single compound is formed by the
direct union of two or more substances
- Decomposition reactions are opposite to combination reactions. In a decomposition reaction a compound breaks down into two or more simple substances by the application of heat or electricity.
- In a displacement reaction an atom or group present in a compound is
replaced by another atom or group, without bringing any change in the
structure of the molecule or compound
- In double displacement
reactions two different atoms or groups of atoms (ions) of two compounds
exchange their places and give rise to two new compounds
- In a
precipitate reaction insoluble salts are produced
- A reversible
reaction is one that can proceed in both the directions depending upon the
conditions of the reaction
- A reversible thermal decomposition
reaction is called thermal dissociation
- Oxidation is a reaction in
which oxygen is added to a substance, or hydrogen is removed from a
substance
- Reduction is a reaction in which oxygen is removed from a
substance, or hydrogen is added to a substance
- Oxidation reactions
cause corrosion on metals and rancidity on food stuffs
|
| |
|
|
| |
|
|
|
|
|
Get FREE Live Tutoring
(No credit card required)
Customer Care
Click to get customer service, technical support and subscription help.
Refer-A-Friend
Get One Month Free!
When you refer a friend
Chemical Reactions and Equations
|
|
|
