Heat capacity: the heat required to raise the temperature of an object by a certain unit of temperature Temperature: a measure of the average energy due to motion of particles in an object Heat: the transfer of energy based on a temperature difference between two objects According to our second law of thermodynamics, the sand would likely become even more spread out and not form a well-ordered, low entropy sandcastle. If we sat on a beach for a hundred years, would a sandcastle would spontaneously appear? Probably not. If there is a sandcastle on the beach, is this a state of high or low entropy? The sandcastle is in a state of low entropy because the sand is in a highly ordered state. The greater the entropy, the more disordered the energy. Entropy states that energy becomes spread out over time, and we can think of entropy as a movement towards a disordered state. Before we look at an example, let’s think about entropy. The second law of thermodynamics states that the total entropy of an isolated system (we’ll define this term in the next section) cannot decrease over time. If W is negative, the surroundings are doing work on the system. If Q is negative, heat is leaving the system. If ∆U is negative, the temperature of the object is decreasing. If W is positive, work is being done by the system on the surroundings. If Q is positive, heat is coming into the system. ∆U is proportional to the temperature of an object, so an increase in ∆U means the temperature of an object is increasing. Radiation: an indirect transfer of heat through electromagnetic waves that does not require the two objects to be in contact Convection: a transfer of heat through the motion of a liquid or gas over another objectģ. Conduction: a direct transfer of heat through contact and without movement of the objectsĢ. We’ve talked about a few different properties of heat, and now we’ll talk about exactly how heat is transferred from one object to another. For example, water and aluminum have different heats of transformation, and you’ll be provided this information by a passage should you need it on the exam. Since these are properties intrinsic to a substance, they will change based on what substance we are looking at. The heat of fusion is the heat of transformation constant for a solid to liquid transformation, and the heat of vaporization is the heat of transformation constant for a liquid to gas transformation. The heat of transformation is an intrinsic property of a substance that defines the energy needed to generate a phase change. These transitions are called phase changes, and they are often represented by a phase change diagram: Similarly, the process of converting water to water vapor (the gaseous form of water) requires heat. Ice is the solid form of water, and the process of converting ice to water requires heat. To understand heat of transformation, let’s look at an example. Heat of transformation is another important thermodynamic term. Instead, we want to know how much heat we need to raise one gram of the chair by 1 °K. If we go back to the chair example, we now don’t care about the entire chair or raising the temperature by 5 ☌. We define specific heat as the amount of heat required to raise one gram of an object by one degree Kelvin (or Celsius). Specific heat is very similar to heat capacity but defines the amount of our “object” and how much we want to raise the temperature of that object. The SI units for heat capacity are joules (J) / kelvin (K), and this makes sense if we remember that joules are a unit for energy while kelvins are a unit for temperature. Heat capacity would tell us how much heat we need in order to make that happen. For example, let’s say our “object” is a chair and we want to raise the temperature by 5 ☌. Heat capacity is the heat required to raise the temperature of an object by a certain unit of temperature. \( \newcommand\), which is just the (negative) area in the pressure–volume plane that is bounded by the closed path.Now that we’ve defined heat, let’s dive into some of its properties.
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