LEARNATHON
III

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Theory:

Is it possible to change the rate of a reaction?
  
Yes, it is possible to change the rate of a reaction. For example, iron rusts faster in acid than in water.
 
Important factors that affect the rate of a reaction are:
 
(i) Nature of the reactants
(ii) Concentration of the reactants
(iii) Temperature
(iv) Catalyst
(v) Pressure
(vi) Surface area of the reactants
 
Nature of the reactants:
 
The reaction between sodium (\(Na)\) and hydrochloric acid (\(HCl\)) is faster than the reaction between sodium and acetic acid (\(CH_3COOH\)). Do you know why? \(HCl\) is a stronger acid than (\(CH_3COOH\)), and thus more reactive. So, the nature of the reactants influences the reaction rate.
 
\(2Na_{(s)} + 2HCl_{(aq)} → 2NaCl_{(aq)}+ H_{2(g)}(Fast)\)

\(2Na_{(s)} + 2CH_3COOH_{(aq)} → 2CH_3COONa_{(aq)}+ H_{2(g)}(Slow)\)
 
Concentration of the reactants:
 
The reaction rate can also be increased by changing the number of reactants. The amount of the substance present in a particular volume of the solution is called ‘Concentration’. The higher the concentration, the more particles per volume exist in it and hence faster the reaction. Granulated zinc reacts faster with \(2\) \(M\) hydrochloric acid than with \(1\) \(M\) hydrochloric acid.
 
Temperature:
 
At higher temperatures, most of the reactions occur faster. Adding heat to the reactants gives them more energy to break the bonds, so the reaction can be sped faster. At normal temperature, calcium carbonate reacts slowly with hydrochloric acid. The reaction rate increases as the reaction mixture is heated.
 
When the reactants are gases, increasing their pressure speeds up the reaction. This is due to the fact that as the pressure is increased, the reacting particles become closer and collide more frequently.
Did you know?
 
We have noticed that food stored at room temperature spoils more quickly than food stored in the refrigerator. The temperature in the refrigerator is lower than at room temperature; hence the reaction rate is slower.
Pressure:
  
When the reactants are gases, increasing their pressure speeds up the reaction. This is due to the fact that as the pressure is increased, the reacting particles become closer and collide more frequently.
 
Catalyst:

A catalyst is a substance that speeds up the rate of a process without being consumed in the reaction. For example, on heating potassium chlorate \(KClO_3\) decomposes into potassium chloride and oxygen gas, but at a slower rate. When manganese dioxide is added, the reaction rate increases.
 
The surface area of the reactants:

When solid reactants are used in a reaction, the powdered form of the reactant reacts quickly. For example, powdered calcium carbonate reacts more quickly with hydrochloric acid than marble pieces. This is because powdering the reactants increases the surface area and collisions between reactant particles release more energy. Thus, the reaction rate is increased.