Calcium Carbonate: Enthalpy and Entropy Difference at Room Temp & 0K

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In summary, there are two forms of calcium carbonate, calcite and aragonite, with standard enthalpy values of -1206.9 kJ/mol and -1207.1 kJ/mol, respectively. They also have standard entropy values of 92.9 kJ/mol and 88.7 kJ/mol. At equilibrium, their delta G is equal to 0, which can be calculated using the equations -1206.9 + T 92.9 = 0 and -1207.1 + T 88.7 = 0. At room temperature (298K), both forms have a delta H of 1.23 x 10^6 j/mol, but at 0 K,
  • #1
stunner5000pt
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CaCO3 (calcium carbonate) has two states

Calcite [tex] \Delta_{f}H^\Phi [/tex] = -1206.9 kJ/mol
and [tex] S_{m}^\Phi [/tex] = 92.9kJ/mol

Aragonite [tex] \Delta_{f}H^\Phi [/tex] = -1207.1 kJ/mol
and [tex] S_{m}^\Phi [/tex] = 88.7 kJ/mol

where H is the standard enthalpy and S means the standard entropy

a) Assuming that [tex] \Delta_{trs} H [/tex] and [tex] \Delta_{trs} S [/tex] are independant of temperature, at what temperature can these two forms exist in equilibrium at one bar

well at equilibrium delta G = 0

and thus 0 = dH + T dS for each one and thus i get two equations

-1206.9 + T 92.9 = 0 and
-1207.1 + T 88.7 = 0

so is that the equilibrium temperature they can both co exist at?

b) Which form is more stable than the other at room temperature (298K) and whcih is more stable as one approaches 0 K??


So both calcite and aragonite i get 1.23 x 10^6 j / mol and then for 0 K i get the standard delta H of fusion so a more negative value would mean that that one is more stable??

c) Give physical reasons in terms of H and S why the two structures have different H and S values.

Well a solid with a lower S (entropy) would mean that it's density is lower and thus it would be easier to break up something that is less dense as opposed to something that is the opposite.
 
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  • #2
H (enthalpy) is related to the energy of the bonds between the atoms and thus it can be said that the two forms of calcium carbonate have different H values because the bonds between the atoms could be arranged differently in each form.
 
  • #3
The difference in H values could be due to the different crystal structures of calcite and aragonite. Calcite has a trigonal crystal structure while aragonite has an orthorhombic crystal structure. These different structures may result in different bonding energies and therefore different enthalpy values. Additionally, the arrangement of atoms in the crystal lattice can also affect the entropy value, as different arrangements can lead to different degrees of disorder.
 

1. What is Calcium Carbonate?

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks, shells of marine organisms, and eggshells. It is also the main component of many antacids and is used in a variety of industrial applications.

2. What is enthalpy?

Enthalpy is a thermodynamic property that measures the total energy of a system. It is often described as the "heat content" of a system and is represented by the symbol H. Enthalpy is typically measured in joules (J) or kilojoules (kJ).

3. What is entropy?

Entropy is a thermodynamic property that measures the disorder or randomness of a system. It is represented by the symbol S and is typically measured in joules per kelvin (J/K). Entropy increases in a closed system over time, meaning that the system becomes more disordered.

4. What is the difference between enthalpy and entropy?

The main difference between enthalpy and entropy is that enthalpy measures the total energy of a system, while entropy measures the disorder or randomness of a system. Enthalpy is a state function, meaning it depends only on the initial and final states of a system, while entropy is a path function, meaning it depends on the specific process taken to reach a certain state.

5. How does the enthalpy and entropy of Calcium Carbonate differ at room temperature and 0K?

At room temperature, the enthalpy of Calcium Carbonate is higher than at 0K, while the entropy is lower. This is because at room temperature, the molecules in Calcium Carbonate are in a more disordered state, leading to a higher enthalpy and lower entropy. However, at 0K, the molecules are in a more ordered, crystalline state, resulting in a lower enthalpy and higher entropy.

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