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Initially, many of them focused on enthalpy changes and hypothesized that an exothermic process would always be spontaneous. That is, by itself the magnitude of the heat flow associated with a process does not predict whether the process will occur spontaneously.įor many years, chemists and physicists tried to identify a single measurable quantity that would enable them to predict whether a particular process or reaction would occur spontaneously. Yet we all know that such a process is very unlikely to occur: heat is always likely to flow from a hot object to a cold one, but never likely to flow in the reverse direction.
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As long as the same amount of thermal energy was gained by the frying pan and lost by the water, the first law of thermodynamics would be satisfied. Suppose that a hot frying pan in a sink of cold water were to become hotter while the water became cooler. Now consider the same process in reverse. This transfer of heat from a hot object to a cooler one obeys the first law of thermodynamics: energy is conserved. Eventually both objects will reach the same temperature, at a value between the initial temperatures of the two objects. If a hot frying pan that has just been removed from the stove is allowed to come into contact with a cooler object, such as cold water in a sink, heat will flow from the hotter object to the cooler one, in this case usually releasing steam. Let’s consider a familiar example of spontaneous change. (In chemistry, the word spontaneous means "very likely to proceed in the forward direction, as written, in order to reach equilibrium.") This information, however, does not tell us whether a particular process or reaction will occur spontaneously. Changes in the internal energy (ΔU) are closely related to changes in the enthalpy (ΔH), which is a measure of the heat flow between a system and its surroundings at constant pressure. The first law of thermodynamics governs changes in the state function we have called internal energy (\(U\)). To understand the relationship between internal energy and entropy.