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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.
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.
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
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.
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.
when system is in equilibrium ,process is reversible
hfg1/temp1=entropy1
All chemical reactions, whether exothermic or endothermic, involve reactants which turn into products.
All chemical reactions, whether exothermic or endothermic, involve reactants which turn into products
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What is the relationship between enthalpy and temperature?
Enthalpy is the amount of energy in a system and when this changes (when a reaction happens), the energy is either released (exothermic) or absorbed (endothermic) and this energy is usually released or absorbed as heat. Therefore when the enthalpy decreases, heat is released from the system making it exothermic. In contrast, when the enthalpy increases, heat is absorbed making it endothermic.
Is enthalpy a state function?
Yes it is state function
What is EEE in thermodynamics?
Energy, Entropy and Efficiency........
Internal energy and enthalpy how differ and relate to each other?
Enthalpy mathematically is the sum of the internal energy and work done in a process.internal energy is the sum of the kinetic energy,potential energy,vibrational energies etc
How do you read pressure enthalpy chart?
by smoking 3 oz of crack and then u will understand it
Is Delta S is the change in enthalpy a measure of randomness?
No, ĪS (change in entropy) and ĪH (change in enthalpy) are not measurements of randomness. Entropy is a measure of the disorder or randomness in a system, while enthalpy is a measure of the heat energy of a system. The change in entropy and enthalpy can be related in chemical reactions to determine the overall spontaneity of the process.
What characteristics of a substance is NOT affected by enthalpy and entropy?
Pressure is not affected by enthalpy and entropy.pressure
When graphing enthalpy and entropy what variables are included?
In a graph of enthalpy versus temperature, the enthalpy of a substance is plotted on the y-axis, while the temperature is plotted on the x-axis. When graphing entropy versus temperature, the entropy of a substance is plotted on the y-axis while the temperature is plotted on the x-axis.
What is the definition of enthalpy and entropy?
Enthalpy is the amount of energy released or used when kept at a constant pressure. Entropy refers to the unavailable energy within a system, which is also a measure of the problems within the system.
What could make delta G become negative at a given enthalpy and entropy?
For delta G to become negative at a given enthalpy and entropy, the process must be spontaneous. This can happen when the increase in entropy is large enough to overcome the positive enthalpy, leading to a negative overall Gibbs free energy. This typically occurs at higher temperatures where entropy effects dominate.
How do you know if a reaction is entropy driven enthalpy driven or driven by both enthalpy and energy?
An entropy-driven reaction is one where the products have higher entropy than the reactants. An enthalpy-driven reaction is one where the products have lower enthalpy than the reactants. If both the entropy and enthalpy of the products are more favorable than the reactants, it is driven by both enthalpy and entropy.
How does gibbs energy relate to the changes in ethalpy and ethropy?
Gibbs energy accounts for both enthalpy (heat) and entropy (disorder) in a system. A reaction will be spontaneous if the Gibbs energy change is negative, which occurs when enthalpy is negative (exothermic) and/or entropy is positive (increased disorder). The relationship between Gibbs energy, enthalpy, and entropy is described by the equation ĪG = ĪH - TĪS, where T is temperature in Kelvin.
What could make G become negative at a given enthalpy and entropy?
Changing the temperature
What is the relationship between the enthalpy h and entropy s of a reaction that is spontaneous at higher temperatures but not at lower temperatures?
The relationship between enthalpy (H) and entropy (S) is described by the Gibbs free energy equation, ĪG = ĪH - TĪS, where ĪG is the change in Gibbs free energy, ĪH is the change in enthalpy, T is the temperature in Kelvin, and ĪS is the change in entropy. For a reaction to be spontaneous at higher temperatures but not at lower temperatures, the entropy term (TĪS) must dominate over the enthalpy term (ĪH) in the Gibbs free energy equation. This suggests that the increase in entropy with temperature plays a more significant role in driving the reaction towards spontaneity than the enthalpy change.
Predict whether the changes in enthalpy entropy and free energy will be positive or negative for the freezing of water and explain your predictions How does temperature affect the spontaneity?
The changes in enthalpy, entropy, and free energy are negative for the freezing of water since energy is released as heat during the process. At lower temperatures, the freezing of water is more spontaneous as the negative change in enthalpy dominates over the positive change in entropy, making the overall change in free energy negative and leading to a spontaneous process.
What are the units of enthalpy?
The units for entropy are joules per kelvin (J K-1)
What conditions make delta G always positive?
G is always positive when enthalpy increases and entropy decreases.
