شرح و مراجعة Third preparatory sciences
Unit one Chemical reactions
Chemical reactions.
Chemical reaction:
It is the breaking up of bonds in molecules of reactants and forming new bonds in the
molecules of products.
Importance of chemical reactions:
1-Burning of car fuel (gasoline) in car engine
2-Photosynthesis process that depend mainly on the reaction of carbon dioxide with
water.
3-Making medicines, fertilizers and artificial fibers.
They are reactions which involve the breaking up of the compound by the effect of heat
into its simple elements or simpler compounds.
1-Thermal decomposition
Examples on thermal decomposition:
1)Metal hydroxide
2)Metal carbonate
3)Metal sulphate
4)Metal oxide
5)Metal nitrate
Life application on thermal decomposition reactions:
Air Bags
-On occurrence of an accident a rapid decomposition happens to sodium azide forming
sodium and nitrogen gas evolves.
A)Simple substitution
B)Double substitution
They are reactions which depend on the activity of metals where the element which is more active substitute (replace) the less active one in another compound
A) Simple substitution reactions:
They are chemical reactions in which one of the elements substitute another element
in a solution of one of its compounds.
*Metal substitute hydrogen of water or acids
1)Write the scientific term:-
1) The breaking up of bonds in the molecules of the reactant and the formation of new
bonds in the molecules of the new resultants from the reactions.
[ …..…..…………….. ]
2) The reaction between acid and alkali to form salt and water.
[………….……....….. ]
3) A reaction where an element substitutes another one.
[……………….……..]
4) A substance which loses an electron or more during a chemical reaction.
[………...……….….. ]
5) Chemical reaction in which change happens between the two radicals ( ions ) of the
two compounds to form another two compounds. [……………………..]
2) Complete the following statements:-
1) Thermal decomposition reactions involve the ………… …….……… of the
compounds by the effect of …………………….…
2) In the following reaction: H2 + CuO Cu + H2O
copper oxide undergoes …………………….……… process , while hydrogen
undergoes ………… process.
3) …………………… + …………….…… 2 NaCl.
4) During the formation of sodium chloride molecule from its elements, sodium acts as
………………….……… agent while chlorine act as ………………….……… agent.
5) Oxidation and reduction are two …………………….……… processes.
6) Chemical activity series is the arrangement of metals in …………………….………
order according to the degree of their …………………….………
7) Most metal sulphate decomposes by heating into…………………. and ……………
8) From the following reactions, answer the following
first: NaCl + AgNO3 precipitate + + ( B )
Second : ( B ) salt + ( D )
a- Write the symbol of ( B ) and ( D )
b- Write chemical formula of the precipitate and the salt…………………...
c- Mention the kind of each reaction…………………………………..
3) Give reasons for:-
1) The occurrence of effervescence on putting a piece of aluminum in diluted
hydrochloric acid.
……………………………………………………………………………………………
…………………………………………………………….………………….……………
………………………………………………………………………………………….…
2) A white precipitate is formed on adding silver nitrate solution to sodium chloride
solution.
……………………………………………………………………………………………
……………………………………………………………………………….……………
…………………………………………………………………………………………….
3) Although ( Al ) comes before ( Zn ) in chemical activity series but it takes a short
period of time to react with hydrochloric acid .
……………………………………………………………………………………………
………………………………………………………..……………………….…………
…………………………………………………………………………………………….
4) A yellowish white color is formed on heating white sodium nitrate.
……………………………………………………………………………………………
……………………………………………………………………………………………
4)What happens when:-
1) Heating a red mercuric oxide.
……………………………………………………………………………………………
……………………………………….……………………………………………………
…………………………………………………………………………………………….
2) Chlorine atom gains an electron.
……………………………………………………………………………………………
……………………………………………………………………………..….…………
…………………………………………………………………………………………….
3) Adding of dilute HCl to a piece of copper.
……………………………………………………………………………………………
……………………………………….……………………………………………..……
…………………………………………………………………………………………..
5)Write an equation for each of the three next observations of the following
practical experiments:-
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
6)Determine the oxidizing agent and reducing agent in the reaction:
CuO + H2 H2O + Cu
O.A :………………………………
R.A :……………………………....
From the opposite figure, answer the following:-
1. Show by symbolic equations the name of the evolved gas in both tubes ( A ) &
( B )
……………………………………………………………………………………………
……………………………………….………………………………………………….…
……………………………………………………………………………………………..
2. What is the name of the liquid which is formed in tube ( C )?
……………………………………………………………………………………………
……………………………………….………………………………………………..…
…………………………………………………………………………………………..
Factors affecting the speed of chemical reactions
A)Nature of reactants.
B) Concentration of reactants
C) Temperature
D)Catalyst
1-The kind of bonding in reactants
1-Covalent (coordinate) compounds | 2-Ionic compounds |
They are slow reacting compounds | They are fast reacting compounds |
A)Nature of reactants:
Fast reaction because it occurs between ions
2-The surface area of reactants exposed to reaction
*When the surface area increases, the speed of the chemical reaction increases
Example:
Reaction of iron fillings with diluted acid is faster than iron pieces
As the concentration of reactants increases , the number of collisions between molecules
increases so the speed of reaction increases.
Example:
Reaction of magnesium ribbon with concentrated acid is faster than its reaction
with diluted acid.
As the temperature increases, the movement of molecules increases, the number of
collisions increases, the speed of chemical reaction increases
Example:
The reaction of effervescence tablets with hot water is faster than cold water.
It is a substance which speeds up the chemical reaction without changing or being used up.
B) Conc. of reactants:
C) Temperature:
D) Catalyst:
Common factors (properties) of catalyst:
1-They change the speed of reaction but don’t affect either the beginning or stopping
2-They don’t change in mass or chemical properties before or after the reaction
3-They are bonded to the reactants during the reaction but got separated from them
quickly to form the resultant at the end of the reaction
4-They decrease the energy needed for the reaction
5-They are used in a few amounts which are often enough to complete the reaction
1- Complete the following statements :
1- At the end of the reaction , the concentration of ……………………….. becomes
100% while the concentration of ………………………….. becomes zero .
2- Increasing the temperature of the reaction ………..…. The number of
…………………….. between molecules which increase the speed of the reaction .
3- The effervescent tablet reacts with …….….… water slower than the
………..…...water .
2-Write the scientific term:-
1) A substance which increases the speed of the chemical reaction without interfering in
it or being consumed.
[……………………………..]
2) The change in the concentration of the reactants and resultants at a unit time.
[………………....…………..]
3) A catalyst which is used to increase the rate of breaking up of hydrogen peroxide.
[……..………………..……..]
4) Slow reacting compounds. [……..………………..……..]
5) The enzyme which is founds in sweet potato and accelerates the decomposition rate
of hydrogen peroxide. [……………………………..]
3)Give reasons for:-
1) Aluminum wire burns inside a jar filled with oxygen faster than the burning in
atmospheric air
………………………………………………………………………………………..
…………………………………………………………………………………………
2) Food must be heated during its preparation.
……………………………………………………………………………………………
……………………………………………………………………………………………
3) A certain mass of iron filing reacts with acids faster than the reaction of a block of
iron have the same mass with acids.
……………………………………………………………………………………………
…………………………………………………………………………………….....
4) Magnesium reacts with concentrated hydrochloric acid faster than the diluted Sulphuric
acid.
……………………………………………………………………………………………..
……………………………………………………………………………………………..
4)Mention the factors affecting the speed of the chemical reactions.
1- …………………………… 2- ……………………………
3- …………………………… 4- …………………………
5)What is meant by :
- Speed of chemical reaction.
……………………………………………………………………………………………
…………………………………………………………………………………………
7)What happens when:-
1) Putting a piece of sweet potato in a flask containing hydrogen peroxide.
…………………………………………………………………………………………
…………………………………………………………………………………………
2) The concentration of reactants becomes zero.
…………………………………………………………………………………………
…………………………………………………………………………………………
3) Adding sodium hydroxide solution to a blue copper sulphate solution.
……………………………………………………………………………………………
…………………………………………………………………………………………
4- Increasing the temperature of a reaction.
…………………………………………………………………………………………
……………………………………………………………………………………………
8)In this reaction:-
2 H2O2 catalyst 2 H2 O + O2
- Mention the name of the catalyst.
……………………………………………………………………………………………
- What is the role of the catalyst in the reaction ?
………………………………………………………………………………
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