Learning objectives
Section Key Terms
| thermal equilibrium | zeroth law of thermodynamics |
We learned in the previous chapter that when two objects (or systems) are in contact with one another, heat will transfer thermal energy from the object at higher temperature to the one at lower temperature until they both reach the same temperature. The objects are then in thermal equilibrium, and no further temperature changes will occur if they are isolated from other systems. The systems interact and change because their temperatures are different, and the changes stop once their temperatures are the same. Thermal equilibrium is established when two bodies are in thermal contact with each other—meaning heat transfer (i.e., the transfer of energy by heat) can occur between them. If two systems cannot freely exchange energy, they will not reach thermal equilibrium. (It is fortunate that empty space stands between Earth and the sun, because a state of thermal equilibrium with the sun would be too toasty for life on this planet!)
If two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C. This statement may seem obvious, because all three have the same temperature, but it is basic to thermodynamics. It is called the zeroth law of thermodynamics.
You may be wondering at this point, why the wacky name? Shouldn’t this be called the first law of thermodynamics rather than the zeroth? The explanation is that this law was discovered after the first and second laws of thermodynamics but is so fundamental that scientists decided it should logically come first.
As an example of the zeroth law in action, consider newborn babies in neonatal intensive-care units in hospitals. Prematurely born or sick newborns are placed in special incubators. These babies have very little covering while in the incubators, so to an observer, they look as though they may not be warm enough. However, inside the incubator, the temperature of the air, the cot, and the baby are all the same—that is, they are in thermal equilibrium. The ambient temperature is just high enough to keep the baby safe and comfortable.
Check Your Understanding
Source link
What is the zeroth law of thermodynamics?
- Energy can neither be created nor destroyed in a chemical reaction.
- If two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C.
- Entropy of any isolated system not in thermal equilibrium always increases.
- Entropy of a system approaches a constant value as temperature approaches absolute zero.
Section Summary
- Systems are in thermal equilibrium when they have the same temperature.
- Thermal equilibrium occurs when two bodies are in contact with each other and can freely exchange energy.
- The zeroth law of thermodynamics states that when two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system, C, then A is also in thermal equilibrium with C.
Concept Items
When are two bodies in thermal equilibrium?
- When they are in thermal contact and are at different pressures
- When they are not in thermal contact but are at the same pressure
- When they are not in thermal contact but are at different temperatures
- When they are in thermal contact and are at the same temperature
What is thermal contact?
- Two objects are said to be in thermal contact when they are in contact with each other in such a way that the transfer of energy by heat can occur between them.
- Two objects are said to be in thermal contact when they are in contact with each other in such a way that the transfer of energy by mass can occur between them.
- Two objects are said to be in thermal contact when they neither lose nor gain energy by heat. There is no transfer of energy between them.
- Two objects are said to be in thermal contact when they only gain energy by heat. There is transfer of energy between them.
To which mathematical property is the zeroth law of thermodynamics similar?
- Associative property
- Commutative property
- Distributive property
- Transitive property
Critical Thinking
What are the necessary conditions for energy transfer by heat to occur between two bodies through the process of conduction?
- They should be at the same temperature, and they should be in thermal contact.
- They should be at the same temperature, and they should not be in thermal contact.
- They should be at different temperatures, and they should be in thermal contact.
- They should be at different temperatures, and they should not be in thermal contact.
Oil is heated in a pan on a hot plate. The pan is in thermal equilibrium with the hot plate and also with the oil. The temperature of the hot plate is 150 °C . What is the temperature of the oil?
- 160 °C
- 150 °C
- 140 °C
- 130 °C
Test Prep Multiple Choice
Source link
Name any two industries in which the principles of thermodynamics are used.
- aerospace and information technology (IT) industries
- industrial manufacturing and aerospace
- mining and textile industries
- mining and agriculture industries
Test Prep Short Answer
What does green energy development entail?
- Green energy involves finding new ways to harness clean and renewable alternative energy sources.
- Green energy involves finding new ways to conserve alternative energy sources.
- Green energy involves decreasing the efficiency of nonrenewable energy resources.
- Green energy involves finding new ways to harness nonrenewable energy resources.
Why are the sun and Earth not in thermal equilibrium?
- The mass of the sun is much greater than the mass of Earth.
- There is a vast amount of empty space between the sun and Earth.
- The diameter of the sun is much greater than the diameter of Earth.
- The sun is in thermal contact with Earth.
Test Prep Extended Response
Source link
Glossary
- thermal equilibrium
- condition in which heat no longer transfers energy between two objects that are in contact; the two objects have the same temperature
- zeroth law of thermodynamics
- states that if two objects are in thermal equilibrium, and a third object is in thermal equilibrium with one of those objects, it is also in thermal equilibrium with the other object