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First and second law of thermodynamics

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1. For the following processes, state whether the driving force is the first or second law of thermodynamics. The systems are in italics and we are only interested in whether the properties of the system have changed. Explain your choice in 1-2 sentences.

a. Warming up exercises when muscles are worked the cells "burn" more glucose and the oxidation releases energy which is stored as ATP. However only about 50% is stored and the rest increases the temperature of the muscle tissue.
b. You observe the trees in the forest do not grow in straight lines. Forests that were plants by the CCC camps in the Great Depression have the trees plants in long straight rows. Anyone visiting these knows immediately that this is not a natural forest.
2. 12.0L of monoatomic ideal gas at 15◦C and 4atm are expanded to a final pressure of 1.2atm. Calculate ∆U, q, w, and ∆S if the process is:
a. Reversible and isothermal
i. Prove that for the process in part b ∆S is zero.
d. Explain, in 3-4 sentences, why ∆S is different in all three parts
3. The following equation is an equation of state for an imagined gas: . The term accounts for the attractions between the gas molecules. Determine ?

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Hi,

1. For the following processes, state whether the driving force is the first or second law of thermodynamics. The systems are in italics and we are only interested in whether the properties of the system have changed. Explain your choice in 1-2 sentences.

a. Warming up exercises when muscles are worked the cells "burn" more glucose and the oxidation releases energy which is stored as ATP. However only about 50% is stored and the rest increases the temperature of the muscle tissue.

This is an example of the first law of thermodynamics. The first law of thermodynamics is a version of the law of conservation of energy applied on thermodynamics systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed. In our example we have energy that is stored in the form of ATP and our body can use part of that energy for doing some work and part of energy is released as heat.

b. You observe the trees in the forest do not grow in straight lines. Forests that were plants by the CCC camps in the Great Depression have the trees plants in long straight rows. Anyone visiting these knows immediately that this is not a natural forest.

This is an example of the second law of thermodynamics. The second law of thermodynamics states that for some thermodynamic process to occur, entropy of the thermodynamic system and its surroundings must increase. Entropy can be understood as a measure of molecular disorder within a macroscopic system. Spontaneous processes (most natural processes are spontaneous) are characterized by an increase in entropy. In our example trees in the natural forest do not grow in straight lines because that followed by an increase in entropy and system is more disorder and chaotic. To get trees in straight rows (to decrease disorderness or entropy of the system) we had to consume some energy and do some work.

2. 12.0L of monoatomic ideal gas at 15◦C and 4atm are expanded to a final pressure of 1.2atm. Calculate ∆U, q, w, and ∆S if the process is:
a. Reversible and isothermal
i. Prove that for the process in part b ∆S is zero.
d. Explain, in 3-4 sentences, why ∆S is different in all three parts

a)

From ideal gas law we can calculate

When we have isothermal process all heat that system gets is spent on work. So we have:

- negative work because we have expansion. We suppose that

Change of entropy for gas in reversible isothermal process is:
.

Change of entropy in surroundings is the same but with opposite sign, so total entropy change in reversible process will be zero,

b)

When we have adiabatic process, than . It follows . for monoatomic ideal gas is

i)

Definition of entropy is .

We know from entropy definition that there must be some heat change, but as we know for adiabatic process change of heat, or heat transfer is 0, . Therefore, for reversible adiabatic process it is , or in integral form .

c)

In this case, when we have irreversible adiabatic process, will not be zero. We have temperature of the system will change but we do not know how because we were given just the final pressure. All we can see in this particular case is that

d)

Let's consider first change of entropy in reversible and irreversible thermodynamic process. In reversible process change of total entropy will always be zero because system is going from initial to final state reversible (very slow expansion, system is always in thermodynamic equilibrium). In irreversible process change of total entropy will always be greater than zero, for example in adiabatic process in part c, change of heat will be zero, but all work done by gas because of expansion will cause change of internal energy, and therefore decrease of the system temperature.

In reversible isothermal process change of entropy of the system is bigger than change of entropy in reversible adiabatic process. For system to have constant temperature during expansion, it will give heat to surroundings and entropy (or measure of chaos in the system) will change.

3. The following equation is an equation of state for an imagined gas: . The term accounts for the attractions between the gas molecules. Determine ?

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