Internal Energy The First Law of Thermodynamics

Benjamin Thompson, Count Rumford, 1753-1814, was an American-Brltlsh physicist who abandoned his family and left America after the American revolution because of his royalist sympathies. He pursued a checkered career in various countries, including Bavaria (where he ingratiated himself with the Elector of Bavaria), France (where he married Lavoisier s widow), and England (where he founded the Royal Institution and hired Humphrey Davy as a lecturer). 

Julius Robert Mayer, 1814-1878, was a German physicist originally trained as a physician. He was apparently the first to assert that heat and work are two different means by which energy is transferred, and that energy can neither be created nor destroyed. 

Based on the experiments of Rumford, Mayer, Helmholtz, Joule, and many others since the time of Joule, we now state h first law of thermodynamics as it applies to a system whose kinetic and potential energy do not change For a closed system and for any process that begins and ends with equilibrium states 

Hermann Ludwig von Helmholtz, 1821-1894, was a German physicist and physiologist who studied the energy of muscle contraction and who was one of the first to propose that the energy for all processes on the earth ultimately came from solar radiation. 

In spite of the work of Rumford, Mayer, and Joule the credit for announcing the first law of thermodynamics went to Helmholtz. 

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When applied to closed (constant-mass) systems for which the only form of energy that changes is the internal energy, the first law of thermodynamics is expressed mathematically as... 

It will be instructive to look now a little more closely at internal energy. The first law of thermodynamics is formulated in differential form as... 

We would like to generalize our experience with the directionality of nature (and the limits of reversibility) into a quantitative statement that allows us to do calculations and draw conclusions about what is possible, what is not possible, and whether we are close to or far away from the idealization represented by a reversible process. Indeed, it would be nice if we had a thermodynamic property (i.e., a state function) which would help us to quantify directionality, just as internal energy, it, was central in quantifying the conservation of energy (the first law of thermodynamics). It turns out the thermodynamic property entropy, s, allows us to accomplish this goal. 

The classical formulation of the first law of thermodynamics defines the change dU in the internal energy of a system as the sum of heat dq absorbed by the system plus the work dw done on the system ... 

Apphed to a closed system which undergoes only an internal energy change, the first law of thermodynamics is given by equation 1 ... 

In the same way that the first law of thermodynamics cannot be formulated without the prior recognition of internal energy as a property, so also the second law can have no complete and quantitative expression without a prior assertion of the existence of entropy as a property. 

It follows directly from the first law of thermodynamics that if a quantity of heat Q is absorbed by a body then part of that heat will do work W and part will be aecounted for by a rise in the internal energy AE of that body, i.e. 

The first law of thermodynamics states that the internal energy of an isolated system is constant. A state function depends only on the current state of a system. The change in a state function between two states is independent of the path between them. Internal energy is a state function work and heat are not. 

According to the first law of thermodynamics the heat Q absorbed by the system may be equated to the change in internal energy plus the work W done by the system... 

Based on the law of conservation of energy, energy balances are a statement of the first law of thermodynamics. The internal energy depends, not only on temperature, but also on the mass of the system and its composition. For that reason, mass balances are almost always a necessary part of energy balancing. 

If this reaction is implemented, for instance, in a calorimeter, an amount of heat, q, will be released and an amount of work, u/, will be carried out by the expansion of the hydrogen gas along with other volume changes. According to the first law of thermodynamics, the change in the internal energy of the system can be written as... 

But back to our subject the first law of thermodynamics deals with energy and is also known as the law of the conservation of energy. It can be formulated as follows The increase in the internal energy of a thermodynamic system is equal to the amount of heat energy added to the system minus the work done by the system on the surroundings. Energy can occur in various forms, for example, chemical,... 

In order to utilise our colloids as near hard spheres in terms of the thermodynamics we need to account for the presence of the medium and the species it contains. If the ions and molecules intervening between a pair of colloidal particles are small relative to the colloidal species we can treat the medium as a continuum. The role of the molecules and ions can be allowed for by the use of pair potentials between particles. These can be determined so as to include the role of the solution species as an energy of interaction with distance. The limit of the medium forms the boundary of the system and so determines its volume. We can consider the thermodynamic properties of the colloidal system as those in excess of the solvent. The pressure exerted by the colloidal species is now that in excess of the solvent, and is the osmotic pressure II of the colloid. These ideas form the basis of pseudo one-component thermodynamics. This allows us to calculate an elastic rheological property. Let us consider some important thermodynamic quantities for the system. We may apply the first law of thermodynamics to the system. The work done in an osmotic pressure and volume experiment on the colloidal system is related to the excess heat adsorbed d Q and the internal energy change d E ... 

The first law of thermodynamics is the application of the conservation of energy principle. In geochemistry, the first law considers that the change in internal energy (dU) is equal to the heat added to the system (dq) plus the work (dw) done on the system ... 

The first law of thermodynamics applied to an adiabatic system may be expressed as the work done on a system by an adiabatic process, which is equal to the increase in its internal energy, and a function of the state of the system. 

The first law of thermodynamics relates the energy conversion produced by chemical reaction of an energetic material to the work acting on a propulsive or explosive system. The heat produced by chemical reaction q) is converted into the internal energy of the reaction product (e) and the work done to the system [w] according to... 

The first law of thermodynamics asserts that energy is conserved during any process. The three major forms of energy for chemical purposes are the internal energy of each substance, the external work due to changes in pressure or volume, and the exchange of heat with the surroundings. 

The first law of thermodynamics also tells you that if no work is done on or by the sample, that is, pressure and volume are held constant, any heat flow is counterbalanced by a change in internal energy. An exothermic reaction releasing heat to the surroundings, therefore, is accompanied by a decrease in internal energy, whereas an endothermic reaction has a concomitant increase in internal energy. 

According to the First Law of Thermodynamics, Aq = AE -1- w where q is heat, E is the internal energy of the system, and w is work done by the system. If no heat is added to the system (heat was transferred to maintain the initial temperatnre of 300K), then... 

The first law of thermodynamics simply says that energy cannot be created or destroyed. With respect to a chemical system, the internal energy changes if energy flows into or out of the system as heat is applied and/or if work is done on or by the system. The work referred to in this case is the PV work defined earlier, and it simply means that the system expands or contracts. The first law of thermodynamics can be modified for processes that take place under constant pressure conditions. Because reactions are generally carried out in open systems in which the pressure is constant, these conditions are of greater interest than constant volume processes. Under constant pressure conditions Equation 3 can be rewritten as... 

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