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Chapter 5: Problem 23

(a) According to the first law of thermodynamics, what quantity is conserved? (b) What is meant by the internal energy of a system? (c) By what means can the internal energy of a closed system increase?

Short Answer

Expert verified
(a) The conserved quantity in the first law of thermodynamics is the total energy (including internal energy, work, and heat) of the isolated system. (b) Internal energy is the energy associated with the microscopic components of a system, including kinetic and potential energy of atoms and molecules. (c) The internal energy of a closed system can increase through heat transfer from an external source or by mechanical work done on the system.

Step by step solution

01

a) Determine the conserved quantity in the first law of thermodynamics

According to the first law of thermodynamics, energy can neither be created nor destroyed, but it can only be transformed from one form to another in an isolated system. This law is essentially the conservation of energy principle. So, the conserved quantity in the first law of thermodynamics is the total energy (including internal energy, work done by or on the system, and heat exchanged) of the isolated system.
02

b) Define internal energy of a system

The internal energy of a system refers to the energy that is associated with the microscopic components (atoms and molecules) of the system. It includes the kinetic energy (energy of motion) and potential energy (energy due to position or interactions) of the microscopic particles in the system. Internal energy is often considered as a function of temperature, volume, and the number of particles within the system.
03

c) Identify the means to increase the internal energy of a closed system

There are two main means by which the internal energy of a closed system can increase: 1. Heat transfer: If heat is transferred to the system from an external source, the internal energy of the system will increase as the temperature of the system rises. 2. Work done on the system: If mechanical work is done on the system, the internal energy of the system increases as the energy is transferred to internal energy. For example, if a piston compresses a gas inside a cylinder, the temperature of the gas increases, and so does the internal energy of the system.

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Most popular questions from this chapter

In a thermodynamic study, a scientist focuses on the properties of a solution in an apparatus as illustrated. A solution is continuously flowing into the apparatus at the top and out at the bottom, such that the amount of solution in the apparatus is constant with time. (a) Is the solution in the apparatus a closed system, open system, or isolated system? (b) If the inlet and outlet were closed, what type of system would it be?

Consider the decomposition of liquid benzene, \(\mathrm{C}_{6} \mathrm{H}_{6}(l),\) to gaseous acetylene, \(\mathrm{C}_{2} \mathrm{H}_{2}(g) :\) $$\mathrm{C}_{6} \mathrm{H}_{6}(l) \longrightarrow 3 \mathrm{C}_{2} \mathrm{H}_{2}(g) \quad \Delta H=+630 \mathrm{kJ}$$ (a) What is the enthalpy change for the reverse reaction? (b) What is \(\Delta H\) for the formation of 1 mol of acetylene? (c) Which is more likely to be thermodynamically favored, the forward reaction or the reverse reaction? (d) If \(\mathrm{C}_{6} \mathrm{H}_{6}(g)\) were consumed instead of \(\mathrm{C}_{6} \mathrm{H}_{6}(l),\) would you expect the magnitude of \(\Delta H\) to increase, decrease, or stay the same? Explain.

(a) What is meant by the term state function? (b) Give an example of a quantity that is a state function and one that is not. (c) Is the volume of a system a state function? Why or why not?

(a) What is meant by the term fuel value? (b) Which is a greater source of energy as food, 5 g of fat or 9 g of carbohydrate? (c) The metabolism of glucose produces \(\mathrm{CO}_{2}(g)\) and \(\mathrm{H}_{2} \mathrm{O}(l) .\) How does the human body expel these reaction products?

Diethyl ether, \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}(l),\) a flammable compound that was once used as a surgical anesthetic, has the structure $$\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{O}-\mathrm{CH}_{2}-\mathrm{CH}_{3}$$ The complete combustion of 1 mol of \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}(l)\) to \(\mathrm{CO}_{2}(g)\) and \(\mathrm{H}_{2} \mathrm{O}(l)\) yields \(\Delta H^{\circ}=-2723.7 \mathrm{kJ}\) . (a) Write a balanced equation for the combustion of 1 \(\mathrm{mol}\) of \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}(l) .\) (b) By using the information in this problem and data in Table \(5.3,\) calculate \(\Delta H_{f}^{\circ}\) for diethyl ether.
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