For each of the following cases choose a suitable system, if possible, and describe its boundaries and surroundings. Indicate if the work done (Wk) is positive, negative, or zero, and heat transfer (Q), if any, positive, negative or zero.

A balloon is inflated by means of a hand pump. Assume that the balloon, pump, and connectors are adiabatic.

A liquid moving inside a rigid vessel comes slowly to rest.

Hydrogen (H2) and oxygen (O2) in a rigid vessel undergo a chemical reaction and water is formed.

A pressure cooker containing water is put on a stove and the pressure inside rises.

An electric capacitor is connected to a battery.

The voltage across the capacitor is rising.

Question

Engineering

Ronin Rangel

15 April, 14:38

For each of the following cases choose a suitable system, if possible, and describe its boundaries and surroundings. Indicate if the work done (Wk) is positive, negative, or zero, and heat transfer (Q), if any, positive, negative or zero.

A balloon is inflated by means of a hand pump. Assume that the balloon, pump, and connectors are adiabatic.

A liquid moving inside a rigid vessel comes slowly to rest.

Hydrogen (H2) and oxygen (O2) in a rigid vessel undergo a chemical reaction and water is formed.

A pressure cooker containing water is put on a stove and the pressure inside rises.

An electric capacitor is connected to a battery.

The voltage across the capacitor is rising.

+2

Answers (1)

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Rayleen · Answer 1

a.) the balloon outer layer is the boundary. Since balloon, pump and connectors are adiabatic, heat transfer is zero. The work done by the balloon is negative.

b.) the surface of vessel is boundary and everything else is surrounding. work done is zero (since no change is volume). the water gets heated though the change is temperature is very small because of change of kinetic energy to thermal energy.

c.) the container in which reaction takes place is the system and the surface of container is the boundary. Everything outside the container is surrounding. This is an an exothermic reaction, a reaction that release heat. It is also a combustion reaction, where a substance (in this case hydrogen gas) is combined with oxygen.

Work done = 0, in this case (no change in volume of container)

d.) cooker is the system and it's surface the boundary. Heat is added to the system. Work done = 0 (no volume change of cooker)

e.) let us consider the capacitor and battery along with connecting wires as the system. The boundary in this case will be imaginary, everything else will be considered as surrounding. eat is added to the system (the connecting wires get hot). work done is positive (work is done by battery (+ve), w = vq, where v is the potential difference of the battery and q is the charge flowing through it. this work is stored in form of energy of capacitor (1/2 cv2)