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Question : How does chemical processes occur ? Which kind of changes are observed in it ?

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Solution :Chemical COMPOUNDS undergo two types of changes :
(1) Physical change : Change in shape without breaking of bonds.
In another type of physical change there is a change in a state of matter e.g. ice molts into water or water becomes a vapour. These are physical processes.
(2) Chemical change : When bonds are broken and new bonds are formed during transformation, is called a chemical reaction.
e.g. `Ba(OH)_2 + H_2SO_4 toBaSO_4 + 2H_2O`
Above mentioned reaction is inorganic chemical reaction.
Hydrolysis of starch into glucose is an organic chemical reaction.
RATE of a physical or chemical process refers to the amount of product formed per unit time.
Rate `=(deltap)/(deltat)`
Rate can ALSO be called velocity if the direction is specified.
Rates of physical and chemical processes are influenced by temperature
RULE of thumb is that the rate doubles or decreases by half every 10°C change in either direction.
Catalysed reactions proceed at rates much higher than uncatalysed ones.
e.g. `underset("carbon dioxide")(CO_(2)) + underset("water")(H_(2)O) overset("Carbonic anhydrase") In the absence of any enzyme this reaction is very slow, with about 200 molecules of `H_2CO_3` being formed in an hour. However, in the presence of carbonic anhydrase enzyme, 6 million molecules of `H_2CO_3` formed every second.
The enzyme has accelerated the reaction rate by about 10 million times.
There are thousands of types of enzymes each catalysing a unique chemical or metabolic reaction. A multistep chemical reaction, when each of the steps is catalysed by the same enzyme complex or different enzymes, is called a metabolic pathway.
Glucose `to 2` Pyruvic acid
`C_(6)H_(12)O_(6) to 2C_(3)H_(4)O_(3) + 2H_(2)O`
This is actually metabolic pathway in which glucose becomes pyruvic acid through 10 different enzyme catalysed metabolic reactions. When you study respiration in Chapter 14 you will study these reactions.
This very metabolic pathway with one or two additional reactions gives rise to a variety of metabolic end products.
In skeletal muscle, under anaerobic conditions, pyruvic acid is formed. In yeast, during FERMENTATION, the same pathway leads to the production of ethanol in different conditions different products are formed.


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