Practice Problems

Laws of Thermodynamics

Foundations of the Laws of Thermodynamics

The field of thermodynamics deals with systems that are able to transfer thermal energy into at least one other form of energy (mechanical, electrical, etc.) or into work. The laws of thermodynamics were developed over the years as some of the most fundamental rules which are followed when a thermodynamic system goes through some sort of energy change.

Consequences of the Laws of Thermodynamics

The laws of thermodynamics tend to be fairly easy to state and understand... so much so that it's easy to underestimate the impact they have. Among other things, they put constraints on how energy can be used in the universe. It would be very hard to over-emphasize how significant this concept is. The consequences of the laws of thermodynamics touch on almost every aspect of scientific inquiry in some way.

Key Concepts for Understanding the Laws of Thermodynamics

To understand the laws of thermodynamics, it's essential to understand some other thermodynamics concepts that relate to them.

Laws of Thermodynamics:

• Zeroeth Law of Thermodynamics - Two systems each in thermal equilibrium with a third system are in thermal equilibrium to each other.

Zeroeth Law of Thermodynamics

Оно утверждает, что изолированная термодинамическая система с течением времени самопроизвольно переходит в состояние термодинамического равновесия и остаётся в нём сколь угодно долго, если внешние условия сохраняются неизменными

Two systems in thermal equilibrium with a third system are in thermal equilibrium to each other.

This zeroeth law is sort of a transitive property of thermal equilibrium. The transitive property of mathematics says that if A = B and B = C, then A = C. The same is true of thermodynamic systems that are in thermal equilibrium.

One consequence of the zeroeth law is the idea that measuring temperature has any meaning whatsoever. In order to measure a temperature, thermal equilibrium much be reached between the thermometer as a whole, the mercury inside the thermometer, and the substance being measured. This, in turn, results in being able to accurately tell what the temperature of the substance is.

This law was understood without being explicitly stated through much of the history of thermodynamics study, and it was only realized that it was a law in its own right at the beginning of the 20th century. It was British physicist Ralph H. Fowler who first coined the term "zeroeth law," based on a belief that it was more fundamental even than the other laws.

Practice Problems

1. A water at 20 C with mass = 10 kg was poured Into 1,5 kg aluminium boiler. Calculate the amount of heat on order to boil water.
2. 20 L of water at 80º C is added to 10 L of water at 5º C. When water was mixed up temperature became – 55 C. Calculate the amount of heat, taken away from hot water and transferred to cold water

Q= 2,1 10 6 jl

1. Into smelt furnace was put 2000 kg of cast iron at 20 C. Calculate the amoun of heat requied to smelt? Specific heat capacity – 0,54 10 3 jl\kg, heat of melting – 1,4 10 5 temprature of melting of cast iron – 1150 C

Q1 = (heating) 1,22 10 9 jl

Q2 = (melting) 0,28 10 9 jl

Mass of ice = 4500 jl

1. What is the temperature of the water when it reaches thermal equilibrium?

Answer: 46.36º C

• First Law of Thermodynamics - The change in the energy of a system is the amount of energy added to the system minus the energy spent doing work.

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