Enthalpy is a measure of heat content of the system, whereas entropy is the measure of change in (enthalpy/temperature).
To understand why entropy is defined, consider these two cases:
Case 1: An object is kept at room temperature, i.e. 298K, and its temperature is increased to 398K by addition of heat.
Case 2: There is an object at 1000K and the temperature is increased to 1100K.
In both cases, heat addition will almost be same, and so will be the enthalpy change. But in first case there is a change of 25% and in second one, just 10%. So we require another term, which is entropy.
We can understand this by a simple analogy. Suppose you have Rs. 100 with you. If someone gives you a Rs. 50 note, it will make a difference. If you have Rs. 1,00,00,000 with you and someone gives you Rs. 50, though the change is same, it will not even matter to you. So, we require another term to measure the difference made to you by this 50 rupee note.
We can divide the change with the amount you have initially. In first case it is 50/100=0.5. In second case, it is 50/1,00,00,000=0.000005.
In thermodynamics, this ratio is called entropy: change in enthalpy divided by temperature, since temperature is a measure of enthalpy of a system.
Sometimes, entropy is also defined as a measure of randomness of a system, as visible change in randomness of a system tends to decrease with increasing temperature, which can also be well understood by that 50 rupees analogy.
To understand why entropy is defined, consider these two cases:
Case 1: An object is kept at room temperature, i.e. 298K, and its temperature is increased to 398K by addition of heat.
Case 2: There is an object at 1000K and the temperature is increased to 1100K.
In both cases, heat addition will almost be same, and so will be the enthalpy change. But in first case there is a change of 25% and in second one, just 10%. So we require another term, which is entropy.
We can understand this by a simple analogy. Suppose you have Rs. 100 with you. If someone gives you a Rs. 50 note, it will make a difference. If you have Rs. 1,00,00,000 with you and someone gives you Rs. 50, though the change is same, it will not even matter to you. So, we require another term to measure the difference made to you by this 50 rupee note.
We can divide the change with the amount you have initially. In first case it is 50/100=0.5. In second case, it is 50/1,00,00,000=0.000005.
In thermodynamics, this ratio is called entropy: change in enthalpy divided by temperature, since temperature is a measure of enthalpy of a system.
Sometimes, entropy is also defined as a measure of randomness of a system, as visible change in randomness of a system tends to decrease with increasing temperature, which can also be well understood by that 50 rupees analogy.
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