What is the significance of the first law of thermodynamics

We shall see this again in later sections of this chapter. For example, in the topic of entropy, calculations will be made using the atomic and molecular view. To get a better idea of how to think about the internal energy of a system, let us examine a system going from State 1 to State 2. The system has internal energy U 1 in State 1, and it has internal energy U 2 in State 2, no matter how it got to either state.

By path, we mean the method of getting from the starting point to the ending point. Why is this independence important?

This path independence means that internal energy U is easier to consider than either heat transfer or work done. Figure 3. Two different processes produce the same change in a system. If the system starts out in the same state in a and b , it will end up in the same final state in either case—its final state is related to internal energy, not how that energy was acquired. In part 1, we must first find the net heat transfer and net work done from the given information.

In part b , the net heat transfer and work done are given, so the equation can be used directly. The net heat transfer is the heat transfer into the system minus the heat transfer out of the system, or. We can also find the change in internal energy for each of the two steps. First, consider No matter whether you look at the overall process or break it into steps, the change in internal energy is the same.

A very different process in part 2 produces the same 9. The system ends up in the same state in both parts. Parts 1 and 2 present two different paths for the system to follow between the same starting and ending points, and the change in internal energy for each is the same—it is independent of path. Human metabolism is the conversion of food into heat transfer, work, and stored fat.

Metabolism is an interesting example of the first law of thermodynamics in action. We now take another look at these topics via the first law of thermodynamics. Considering the body as the system of interest, we can use the first law to examine heat transfer, doing work, and internal energy in activities ranging from sleep to heavy exercise. What are some of the major characteristics of heat transfer, doing work, and energy in the body?

For one, body temperature is normally kept constant by heat transfer to the surroundings. This means Q is negative.

Another fact is that the body usually does work on the outside world. This means W is positive. Now consider the effects of eating.

Eating increases the internal energy of the body by adding chemical potential energy this is an unromantic view of a good steak. The body metabolizes all the food we consume. Basically, metabolism is an oxidation process in which the chemical potential energy of food is released.

This implies that food input is in the form of work. Food energy is reported in a special unit, known as the Calorie.

This energy is measured by burning food in a calorimeter, which is how the units are determined. In chemistry and biochemistry, one calorie spelled with a lowercase c is defined as the energy or heat transfer required to raise the temperature of one gram of pure water by one degree Celsius. Nutritionists and weight-watchers tend to use the dietary calorie, which is frequently called a Calorie spelled with a capital C.

One food Calorie is the energy needed to raise the temperature of one kilogram of water by one degree Celsius. This means that one dietary Calorie is equal to one kilocalorie for the chemist, and one must be careful to avoid confusion between the two. Again, consider the internal energy the body has lost. There are three places this internal energy can go—to heat transfer, to doing work, and to stored fat a tiny fraction also goes to cell repair and growth.

Heat transfer and doing work take internal energy out of the body, and food puts it back. If you eat just the right amount of food, then your average internal energy remains constant. The reverse is true if you eat too little. This process is how dieting produces weight loss.

Life is not always this simple, as any dieter knows. The body stores fat or metabolizes it only if energy intake changes for a period of several days. Once you have been on a major diet, the next one is less successful because your body alters the way it responds to low energy intake.

Your basal metabolic rate BMR is the rate at which food is converted into heat transfer and work done while the body is at complete rest. The body adjusts its basal metabolic rate to partially compensate for over-eating or under-eating. The body will decrease the metabolic rate rather than eliminate its own fat to replace lost food intake. You will chill more easily and feel less energetic as a result of the lower metabolic rate, and you will not lose weight as fast as before.

Exercise helps to lose weight, because it produces both heat transfer from your body and work, and raises your metabolic rate even when you are at rest. Thus, internal energy increases during the melting process. Consider one mole of gas enclosed in a thermodynamic system fitted with a frictionless piston. Let P, V, T be the pressure, volume, and temperature of the gas.

We know that the formula for one mole of gas heated at a low temperature and constant volume is C V dT. Now, using the ideal gas law equation, i. The first law of thermodynamics does not show the direction in which the change occurs. During winters, when we apply brakes to stop our car, work done against friction converts into heat. However, when it cools down, it does not start moving with the conversion of all its heat energy.

This means that the heat stored should have been utilized in starting the car. This becomes a limitation of this law. There are many reasons which makes the first law of thermodynamics very important. Thus electrical energy of a battery is converted into light energy and heat energy of your device. Display is the light energy and heating of laptop or mobile phone is the heat energy. In this way, the first law of thermodynamics is important to understand the concept of energy conservation.

These atoms and molecules perform various types of motion like rotational motion, vibrational motion, translational motion, etc…. In terms of heat, internal energy and work, the statement of first law of thermodynamics is given as;.

We can find the unknown values from this mathematical equation of the first law of thermodynamics.