Tiêu đề 100 Thermodynamics.pdf ✅

3.1.4. Density of Fluids From the ideal gas law, PV = nRT P = nRT V However, ρ = m V . To get the quantity of mass, the number of moles must be multiplied by the molar mass of the substance, M (in kg mol). P = nRT V ( M M ) P = ( nM V ) ( R M ) T P = ρR ′T where R’ is the characteristic gas constant depending on the substance. 4. Heat Transfer Heat is the internal energy of an object based on the movement of its atoms. The common unit for heat is the calorie, equivalent to 4.184 J. Note that this is not the same as Calorie, which is a nutritional unit and is equivalent to 1000 calories. The unit calorie is based on the amount of heat needed to raise 1 g of water by 1 °C in temperature. The heat (Q) transferred to one substance is directly proportional to its mass and the temperature change. ∆Q ∝ m(∆T) The constant of proportionality when the phase of the material does not change is the specific heat (c) of that material. By definition of calorie, the specific heat of water is one calorie. ∆Q = cm(∆T) When the value of ∆Q is positive, then the heat transfer is endothermic (the material receives heat). If ∆Q is negative, then the heat transfer is exothermic (the material loses heat). 4.1. Latent Heat The changes in the phase of a material can be any of the following: Phase changes are not instant. A certain amount of heat is required to complete the phase change. Thus, the temperature of the material remains the same as long as the phase change is not complete. The latent heat of fusion is the heat required to transfer from the solid phase to the liquid phase (and vice versa). The latent heat of vaporization is the heat required to transfer from the solid phase to the liquid phase (and vice versa). The latent heats of fusion and vaporization of water are 80 cal/g and 540 cal/g, respectively. For example, How much heat is required to boil 10 grams of ice, which is at 0 °C? The heat required to transform the ice to water is 80(10) = 800 cal. The heat required to raise the temperature of the water up to its boiling point is ∆Q = 1(10)(100 − 0) = 1000 cal. The heat required to change the water into its vapor form is 540(10) = 5400 cal. Thus, the total heat required is 7200 cal.