Equation used in workdone6/19/2023 ![]() Where the mass, specific heat, and change in temperature are multiplied together. In this case, the proportionality constant is labeled c and is called the specific heat capacity The proportionality constant between heat, mass, and temperature change also called specific heat., or, more succinctly, specific heat: q = mcΔ T Where ∝ means “is proportional to.” To make a proportionality an equality, we include a proportionality constant. We can write this mathematically as q ∝ m × Δ T Because heat is a measure of energy transfer, heat is also measured in joules.įor a given object, the amount of heat ( q) involved is proportional to two things: the mass of the object ( m) and the temperature change (Δ T) evoked by the energy transfer. If energy is transferred from your hands to the object, your hands feel cold. For example, when we touch something with our hands, we interpret that object as either hot or cold depending on how energy is transferred: If energy is transferred into your hands, the object feels hot. is the transfer of energy from one body to another due to a difference in temperature. Heat The transfer of energy from one body to another due to a difference in temperature. What is the work performed when a gas expands from 0.66 L to 1.33 L against an external pressure of 0.775 atm? We limit the final answer to three significant figures, as appropriate. atmospheres and joules: − 3.47 L ⋅ atm × 101.Now we construct a conversion factor from the relationship between liter Now we can use the definition of work to determine the work done: w = − P ext A change is always the final value minus the initial value: Δ V = V final − V initial = 6.19 L − 3.44 L = 2.75 L What is the work performed by a gas if it expands from 3.44 L to 6.19 L against a constant external pressure of 1.26 atm? Express the final answer in joules.įirst we need to determine the change in volume, Δ V. On the other hand, if the gas is contracting, Δ V is negative, and the two negative signs make the work positive, so energy is being added to the system. The negative sign in the equation for work is important and implies that as volume expands (Δ V is positive), the gas in the system is losing energy as work. This term is always the final volume minus the initial volume, Δ V = V final − V initialĪnd can be positive or negative, depending on whether V final is larger (is expanding) or smaller (is contracting) than V initial. Where Δ V is the change in volume of the gas. Assuming that the external pressure P ext is constant, the amount of work done by the gas is given by the equation w = − P ext × Δ V When a certain volume of a gas expands, it works against an external pressure to expand ( Figure 7.2 "Volume versus Pressure"). It turns out that there are other equivalent definitions of work that are also important in chemistry. ![]() ![]() We have already defined work as a force acting through a distance. Relate the amount of heat to a temperature change.Define a type of work in terms of pressure and volume.
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