Thermo Lesson 3 Notes - Copy PDF

LESSON 3 What is a Pure Substance? Substance that has a fixed chemical composition throughout. A mixture of various chemical elements or compounds also qualifies as a pure substance as long as the mixture is homogeneous. What is a Homogeneous mixture (solutions)? any mixture that is unifor...

LESSON 3 What is a Pure Substance? Substance that has a fixed chemical composition throughout. A mixture of various chemical elements or compounds also qualifies as a pure substance as long as the mixture is homogeneous. What is a Homogeneous mixture (solutions)? any mixture that is uniform in composition throughout. Mixture of liquid and water vapor (pure substance)✅ Mixtures of gases, such as air, as long as there is no change of phase.✅ Mixture of liquid and gaseous air (not a pure substance)✅ What is a Phase? Quantity of matter that is homogeneous throughout in both chemical composition and physical structure. Solid : strong intermolecular bond Liquid : intermediate intermolecular bonds Gas : weak intermolecular bond Phase-Change Process Constant- Pressure Heating Process What is Critical Point? The temperature and pressure above which there is no distinction between the liquid and vapor phases. a point on a phase diagram at which both the liquid and gas phases of a substance have the same density, and are therefore indistinguishable. What is Triple Point? the temperature and pressure at which all three phases can exist in equilibrium. Sublimation – SV Vaporization – LV Condensation – VL Fusion or melting – SL What is Saturation? condition in which a mixture of vapor and liquid can exist together at a given temperature and pressure. For a pure substance there is a definite relationship between saturation pressure and saturation temperature. “The higher the pressure, the higher the saturation temperature.” What is Saturation Pressure? the pressure at which the liquid and vapor phases are in equilibrium at a given temperature. Vapor Pressure Curve  The graphical representation of this relationship between temperature and pressure at saturated conditions. What is a Saturated Liquid? Substance exists as a liquid at the saturation temperature and pressure What is a Sub cooled Liquid/Compressed Liquid? The temperature of the liquid is lower than the saturation temperature for the existing pressure. What is a Saturated Vapor? If a substance exists entirely as vapor at saturation temperature. What is a Superheated Vapor? When the vapor is at a temperature greater than the saturation temperature. [ Pressure and temperature of superheated vapor - are independent properties, - temperature may increase while the pressure remains constant] What is Latent Heat?  amount of energy absorbed or released during a phase-change process. What is Latent Heat of Fusion? amount of energy absorbed during melting. amount of energy released during freezing. What is Latent Heat of Vaporization? amount of energy absorbed during vaporization equivalent to the energy released during condensation. [At 1 atm pressure latent heat of fusion of water: 333.7 kJ/kg latent heat of vaporization: 2256.5 kJ/kg.] What is a Quality (x)? When a substance exists as part liquid and part vapor at saturation condition - ratio of the mass of the vapor to the total mass of both vapor and liquid. What is a Moisture Content?  defined as the ratio of the mass of the liquid to the total mass of both liquid and vapor. Ideal Gas Robert Boyle The pressure of a gas expanding at constant temperature varies inversely to the volume Jacques Charles The pressure of a gas varies directly with temperature when the volume is held constant, and the volume varies directly with temperature when the pressure is held constant [By combining the results of Charles’ and Boyles’ experiments, the relationship can be following obtained: What is an Ideal Gas Constant (R)? The constant in the equation is designated by R. The ideal gas equation becomes In order to make the equation applicable to all ideal gas, a universal gas constant Ru is introduced [Amount of energy needed to raise the temperature of a unit of mass of a substance by one degree] Specific heat at constant volume (Cv), Specific heat at constant pressure (Cp) [Amount of energy needed to raise the temperature of a unit of mass of a substance by one degree] Using the definition of enthalpy (h = u + Pv) and writing the differential of enthalpy, Relationship between the specific heats for ideal gases is: What is the Specific Heat Ratio, (k)? What is Internal Energy, (u)? [For ideal gases u, h, Cv, and Cp, are functions of temperature alone.] The Δu and Δh of ideal gases can be expressed as: