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Work and Heat Are Equivalent Form of Energy

In imperial units, unit work is performed when a weight of 1 lbf (pound force) is lifted vertically against gravity over a distance of 1 foot. The unit is called lb ft. The heat added or removed from a system changes its internal energy (a concept we will discuss in the next section) and therefore its temperature. Such an increase in temperature is observed during cooking. However, adding heat does not necessarily increase the temperature. One example is melting ice; That is, when a substance moves from one phase to another. Working on or from the system can also change the internal energy of the system. Joule showed that the temperature of a system can be increased by agitation. If an ice cube is rubbed on a rough surface, the frictional force is used. A system has a well-defined internal energy, but we cannot say that it has a specific “heat content” or “working content”.

We use the term “heat transfer” to emphasize its nature. The science of calorimetry is used to determine the thermal energy (or calorie) content of a material (in known applications, the energy content of food). Using a device called a bomb calorimeter, a sample is placed in a chamber (known as a bomb) of known heat capacity, which is immersed in water. The water bath is insulated to prevent heat loss to the outside. Oxygen is pumped into the chamber and a spark is used to ignite the sample. After complete combustion, the temperature in the calorimeter reaches a maximum that can be used to calculate the thermal energy content of the sample. Traditionally, the unit of caloric energy is used and is defined as the amount of energy needed to increase one gram of water by one degree Celsius. It is also possible to change the temperature of a substance through work. Work can transfer energy inside or outside a system. This realization helped establish the fact that heat is a form of energy.

James Prescott Joule (1818-1889) conducted numerous experiments to establish the mechanical equivalent of heat – the work required to produce the same effects as heat transfer. In terms of units used for these two terms, the best modern value for this equivalence is 1,000 kcal = 4186 J. We think of this equation as the conversion between two different units of energy. Specific enthalpy is a measure of total energy in a unit mass. The commonly used SI unit is J/kg or kJ/kg. Consider the energy required to heat 1.0 kg of water from 0 oC to 100 oC when the specific heat of water is 4.19 kJ / kgoC: heat is the spontaneous transfer of energy due to a temperature difference. Thermochemistry studies the contribution of chemical processes to thermodynamics, the science of energy transfer. Energy is often (unsatisfactorily) defined as the ability to do a job and can be classified as one of two types. Kinetic energy is kinetic energy, such as that possessed by a baseball thrown from a pitcher, a bullet from a weapon, or a transmitting H2 gas molecule. The potential energy is the energy of the position (technical position in a gradient field”).

The most well-known form of potential energy is gravity, like Newton`s apple when it was suspended in the tree. More relevant to chemistry is the potential energy due to its position in an electric or magnetic field, such as solvated ions or atoms that transfer charges during the formation of compounds or molecules. Another important form of potential energy is that found in a coiled spring. Bonded atoms exhibit strikingly similar behavior (vibrational movements) to feathers. Potential energy is often thought of as “stored” kinetic energy, meaning that bodies remain stationary in a potential field while being held by a force, and when this force changes (for example, breaking the branch holding an apple or breaking the bond between two atoms), the potential energy is converted into kinetic form (the apple “falls” or the molecule “dissociates”). The unit of energy is a derived physical quantity with the dimension energy = mass × length2 × time-2. The SI unit of energy is the joule (J): concerted motion (particles with net motions in a fixed direction) can be harvested to provide energy that is used as work (w). Conversely, energy can be used to induce network movements or to work on a system. Electrons moving through a potential, winding or releasing a spring, and compression fluids (hydraulic action) are examples of processes that may generate or require work. We will look at a fourth type of work in this lesson; This causes an expansion or contraction of a gas against an external resistance called PV work. Heat transfer by temperature difference alone is called heat flow. SI units for heat flow are J/s or watts (W) – the same as power.

One watt is defined as 1 J/s. Specific heat (= specific heat capacity) is the amount of heat required to change the temperature of a unit of mass of a substance by one degree. The total energy of a system is composed of internal, potential and kinetic energy. The temperature of a substance is directly related to its internal energy. Internal energy is associated with the movement, interaction and binding of molecules in a substance. The external energy of a substance is associated with its speed and location and is the sum of its potential and kinetic energy. Now suppose that a 125 g iron block heated to 65.0 oC is thermally brought into thermal contact with a 215 g copper block at 20.0 oC in an adiabatic container. According to the first law: The total amount of energy transferred as heat is usually written as Q for algebraic purposes. The heat that a system releases into its environment is conventionally a negative quantity (Q 0). The amount of mechanical work done can be determined by an equation derived from Newtonian mechanics.

Other units used to quantify heat are the British thermal unit – BTU (the amount of heat to increase 1 pound of water by 1oF) and the calorie (the amount of heat to increase 1 gram of water by 1oC (or 1 K)). Figure 1 shows one of Joules` most famous experimental facilities for demonstrating the mechanical equivalent of heat. He showed that work and heat can produce the same effects, and helped establish the principle of energy saving. Potential gravitational energy (PE) (work done by gravitational force) is converted into kinetic energy (KE) and then randomized by viscosity and turbulence into an increase in the average kinetic energy of the atoms and molecules in the system, resulting in an increase in temperature. His contributions to the field of thermodynamics were so important that the SI unit of energy was named after him.

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