What are the entropy and enthalpy?

Answer 1

Enthalpy is the energy of the molecules. It cannot be measured, although CHANGE in enthalpy of reactions can be measured. It's simply heat energy. Exothermic reactions have anegative enthalpy change(which means energy of the products is lower than that of the reactants). Endothermic reactions have a positive value(energy of products is higher than that of the reactants). Entropy, on the other hand, is the degree of disorder. It's the measurement of how disordered a substance is. For example, particles in a solid are regularly arranged, so they are less disordered, and have a low value of entropy. Gases have much higher entropies. Entropy of an individual compound can be measured/calculated.

Answer 2

ENTHALPHY: Is the energy content of a process (chemical, thermodynamic, mechanical, etc) that can be recovered. It is also described as useful energy.

ENTROPY: Is the energy content of a process (chemical, thermodynamic, mechanical, etc) that CAN NOT be recovered. It is also described as chaos.

Answer 3

The following is a bit about each Enthalpy and Entropy and little bit how and why they are arrived at as such.

Enthalpy is the heat content of a substance.

One CANNOT measure the H (heat) or E(energy)

H= E + (PV)

Heat = Energy + (Pressure X Volume) See, we can't measure energy like this!

But one CAN measure the change in Enthalpy (Delta H). Look:

(Delta)H = (Delta)E + (Delta) PV

Pressure is usually constant..... (makes sense, right?!) so under circumstances when this is the case (being most of the time), the equation will look like this:

(Delta)H = (Delta)E + P(Delta)V

Entropy is a measure of the disorder in a system.

It cannot be measured but the change in Entropy can be measured.

The second law of thermodynamics states: Entropy of the universe is constantly increasing. The universe consists of the system and surroundings.

(Delta)S universe = (delta) S system - (delta) S universe

Since the universe is always expanding, the system entropy change can be positive or negative, and then the change in universe must accommodate to ensure that S universe is always positive (expanding).

Neat, huh?

For the calculation of the change in Entropy for a process use the equation

(Delta) S = S products/initial - Sreactants/final

If the process is spontaneous it will:

1. absorb heat (negative (Delta)H)

2. increase randomness (positive (Delta) S.

So if (Delta)S will be positive then S final > S initial

John E. Mc Murray, Robert C. Fay, Chemistry 5th Edition. 2008. Pgs 278-298

Answer 4

Both entropy (S) and enthalpy (H) are state functions. That is to say they are determined by the state of system (e.g. the values of P, V) and not dependent on how the system got to that state. When a system changes state, the change in enthalpy is related to the change in entropy by dH = TdS + VdP. It follows that H has the units of heat (e.g. calories) and entropy has the units of heat per degree of temperature.

Answer 5

Enthalpy refers to the total energy content of the system. It is represented in thermodynamics as H=E+PV, where H refers to the total enthalpy of the system, E refers to the total internal energy of the system, P referes to the pressure of the system and V refers to the volume of the system. Any change in any of these thermodynamic variables will result in change in enthalpy of the system. Entropy, as my friend had mentioned earlier, is a term for disorder in a system and that the overall entropy in a system always increases.

Answer 6

when system is in equilibrium ,process is reversible

hfg1/temp1=entropy1

Answer 7

All chemical reactions, whether exothermic or endothermic, involve reactants which turn into products.

Answer 8

All chemical reactions, whether exothermic or endothermic, involve reactants which turn into products

Answer 9

Type your answer here...

Answer 10

they involve transfer of thermal energy