Chapter 6 Egan
latent heat of vaporization
The amount of energy required to change a unit mass of a substance from liquid to gas the latent heat of vaporization is the number of calories required to vaporize 1 g of a liquid at its normal boiling point.
Internal Energy of Matter
The atoms that make up all matter are in constant motion at normal temperatures.2 This motion results from internal energy. There are two major types of internal energy: (1) potential energy and (2) kinetic energy.
specific gravity
refers to the ratio of the density of one fluid compared with the density of another reference substance, which is typically water.
Sublimation
term used for the phase transition from a solid to a vapor without becoming a liquid as an intermediary form. An example of sublimation is dry ice (frozen carbon dioxide). This sublimation occurs because the vapor pressure is low enough for the intermediate liquid not to appear.
percent body humidity
the ratio of a saturated gas's actual water vapor content to its capacity for same at body temperature (37°C). The BH is the same as RH except that the capacity (or denomi- nator) is fixed at 43.8 mg/L: BH(%) = Content (mg L)/43.8× 100%
Humidity
a measure of the amount of water vapor in the air
Kinetic Activity of Gases
Because the intermolecular forces of attraction of a gas are so weak, most of the internal energy of a gas is kinetic energy. Kinetic theory says that gas molecules travel about randomly at very high speeds and with frequent collisions. As a gas is warmed, its kinetic activity increases, its molecular collisions increase, and its pressure increases. when a gas is cooled, molecular activity decreases, particle velocity and collision frequency decrease, and the pressure decreases.
Evaporation, Vapor Pressure, and Humidity
Boiling is only one type of vaporization. A liquid can also change into a gas at temperatures lower than its boiling point through a process called evaporation. After water is converted to a vapor, it acts like any gas. Not to be confused with visible particulate water, such as mist or fog, this invisible gaseous form of water is called molecular water.
Capillary Action
Capillary action is a phenomenon in which a liquid in a small tube moves upward, against gravity. Capillary action involves both adhesive and surface tension forces. a small capillary tube creates a more concave meniscus and a greater area of contact, liquid rises higher in tubes with smaller cross-sectional areas The concept of capillary action can be seen in many small-volume jet nebulizers. Inside of the nebulizer chamber there is a thin fluid pathway allowing capillary action to bring the medication up from the reservoir.
Condensed
Condensed moisture deposits on any available surface, such as on the walls of a container or delivery tubing or on particles suspended in the gas. Condensation returns heat to and warms the surrounding environment, whereas vaporization of water cools the adjacent air.
Conduction
Conduction is the transfer of energy by direct contact between hot and cold molecules.
Liquid-Vapor Phase Changes
Only after ice completely melts does additional heat increase the temperature of the newly formed liquid. As the water temperature reaches 100°C, a new change of state begins—from liquid to vapor. This change of state is called vaporization. There are two different forms of vaporization: boiling and evaporation.
potential energy
Potential energy is referred to as the energy of position—that is, the energy possessed by an object balanced on a shelf. Potential energy is a result of the strong attractive forces between molecules. These intermolecular forces are why solids are rigid and liquids have viscosity and cohesiveness.
Radiation
Radiation is another mechanism for heat transfer. radiant heat transfer occurs without direct physical contact. Heat transfer by radiation occurs even in a vacuum, as when the sun warms the earth. Objects such as an electrical stove burner or a kerosene heater radiate some of their energy as visible light. In the clinical setting, radiant heat energy is commonly used to keep newborn infants warm.
surface tension
Surface tension always forces a liquid have the small- est possible surface area. That is why aerosol droplets are round. A sphere has the smallest surface area.
Influence of temperature
Temperature affects evaporation in two ways. First, the warmer the air, the more vapor it can hold. Specifically, the capacity of air to hold water vapor increases with temperature. The warmer the air contacting a water surface, the faster is the rate of evaporation. Second, if water is heated, its kinetic energy is increased and more molecules are helped to escape from its surface Last, if the container of heated water is covered, the air again becomes saturated The temperature of a gas affects both its capacity to hold molecular water and the water vapor pressure.
Temperature
Temperature is a measurement of heat. Heat is the result of molecules colliding with one another.
Molar volume
The Avogadro's law states that equal volumes of gases under the same conditions must contain the same number of molecules. At a constant temperature and pressure, 1 mole of a gas should occupy the same volume as 1 mole of any other gas. This ideal volume is termed the molar volume. At standard temperature (0.0°C) and pressure (760 mm Hg) dry (STPD); the ideal molar volume of any gas is 22.4 L. In reality there are small deviations from this ideal. For example, although the molar volumes of both O2 and nitrogen are 22.4 L at STPD, the molar volume of CO2 is closer to 22.3 L.
Discuss three common temperature scales and how to convert from one system to another
The Fahrenheit and Celsius scales are based on properties of water (freezing and boiling). A third scale, the Kelvin scale, is based on molecular motion. K = °C + 273 Conversely, to convert degrees Kelvin to degrees Celsius, you simply subtract 273. K-273=C To convert degrees Fahrenheit to degrees Celsius, use the following formula: °C = (°F − 32) 1.8 To convert degrees Celsius to degrees Fahrenheit, simply reverse this formula: °F = (1.8 × °C) + 32
Cohesion and Adhesion
The attractive force between like molecules is called cohesion. The attractive force between unlike molecules is called adhesion.
Boiling
The boiling point of a liquid is the temperature at which its vapor pressure exceeds atmospheric pressure. When a liquid boils, its molecules must have enough kinetic energy to force themselves into the atmosphere against the opposing pressure. Because the weight of the atmosphere retards the escape of vapor molecules, the greater the ambient pressure, the greater is the boiling point Although boiling is associated with high temperatures, the boiling points of most liquefied gases are very low. At 1 atm, O2 boils at −183°C.
Absolute Zero
absolute zero is the lowest possible temperature that can be achieved. no kinetic energy. Because there is no energy, the molecules cease to vibrate and the object has no heat that can be measured. due to the third law of thermodynamics, which states that absolute zero is impossible to achieve.
hygrometers
allow measurement of RH using a wide variety of ingenuous mechanisms based on the effects of humidity on, for example, temperature through evaporation (psychrometers), the length of a human hair, or electrical capacitance and resistance.
Absolute humidity
can be measured by weighing the water vapor extracted from air using a drying agent.
dewpoint
temperature at which water vapor condenses back to its liquid form. Cooling a saturated gas below its dew point causes increasingly more water vapor to condense into liquid water droplets. The larger the glass, the greater is its capacity. The water in the glasses represents the actual water vapor content. A glass that is half full is at 50% capacity, or 50% RH. A full glass represents the saturated state, which is equivalent to 100% RH.
water vapor pressure
the pressure exerted by water in its gaseous state. If the container is covered, water vapor molecules continue to enter the air until it can hold no more water. At this point, the air over the water is saturated with water vapor. However, vaporization does not stop when saturation occurs. Instead, for every molecule escaping into the air, another returns to the water reservoir. These conditions are referred to as a state of equilibrium.
Laplace's law
the pressure inside the bubble varies directly with the surface tension of the liquid and inversely with its radius. Internal surface tension (T) will attempt to contract the bubble but is opposed by the resulting pressure inside the bubble (P). The law of Laplace defines the relationship between surface tension and the radius of a sphere (the "radius of curvature"): P = 2T/R For a structure such as a soap bubble, which has two liquid-air surfaces (and hence twice the surface tension) the equation is P = 4T/R
Pascal's principle
the pressure of a given liquid is the same at any specific depth (h), regardless of the container's shape. This is because the pressure of a liquid acts equally in all directions.
Thermodynamics
the science of studying the properties of matter at various temperatures or the kinetics (speed) of reactions of matter at various temperatures.
Describe the properties of gases
- Solids have a fixed volume and shape. Solids maintain their shape because their atoms are kept in place by strong mutual attractive forces, called van der Waals forces. - Liquids have a fixed volume but adapt to the shape of their container. forces are much weaker in liquids than in solids, liquid molecules can move about freely. similar to solids, liquids are dense and cannot be compressed easily. -gas, molecular attractive forces are very weak. are easily compressed and expanded. gases can flow. gases are considered fluids. Gases have no fixed volume or shape. - Plasma has been referred to as a fourth state of matter. Plasma is a combination of neutral atoms, free electrons, and atomic nuclei. Plasmas can react to electromagnetic forces and flow freely, similar to a liquid or a gas
Measuring atmospheric pressure.
A barometer consists of an evacuated glass tube approximately 1 m long. This tube is closed at the top, with its lower, open end immersed in a mercury reservoir. In this manner, the height of the mercury column represents the downward force of atmospheric pressure and is measured in either inches (British) or millimeters (metric). Barometric pressure is reported with readings such as 30.4 inches of mercury (Hg) or 772 mm Hg; this means that the atmospheric pressure is great enough to support a column of mercury 30.4 inches or 772 mm in height the term torr may be used in pressure readings. Torr is short for Torricelli, the seventeenth-century inventor of the mercury barometer. At sea level, 1 torr equals 1 mm Hg. A pressure reading of 772 torr is the same as 772 mm Hg. The pressure exerted by a liquid is directly proportional to its depth (or height) times its density: Pressure = Height × Density
Molar Volume and Gas Density
A major principle governing chemistry is the Avogadro's law. It states that the 1-g atomic weight of any substance contains exactly the same number of atoms, molecules, or ions. 6.023 × 10^23, is the Avogadro's constant.
Density
Density is the ratio of the mass of a substance to its volume. Hydrogen gas is a good example of a low-density substance. Solid or liquid weight density is commonly measured in grams per cubic centimeter. For gases, the most common unit is grams per liter. Because weight density equals weight divided by volume dw O2 = gmw/22.4 = 32/22.4 = 1.43 g/L dw N2 = gmw/22.4 = 28/22.4 = 1.25 g/L dw He = gmw/22.4 = 4/22.4 = 0.179 g/L dw CO2 = gmw/22.4 = 44/22.4 = 1.97 g/L For the density of a gas mixture to be calculated, the percent- age or fraction of each gas in the mixture must be known. To calculate the density of air at STPD, the following equation is used: dw air =(FN×gmwN)+(FO2 ×gmwO2) 22.4L dw air=(0.79×28)+(0.21×32)22.4 dw air=1.29gL
Gaseous Diffusion
Diffusion is the process whereby molecules move from areas of high concentration to areas of lower concentration. Kinetic energy is the driving force behind diffusion. diffusion also occurs in liquids and can occur in solids. Gas diffusion rates are quantified using the Graham's law. Mathematically, the rate of diffusion of a gas (D) is inversely proportional to the square root of its gram molecular weight: Dgas∝ 1/ square root of gmw According to this principle, light gases diffuse rapidly, whereas heavy gases diffuse more slowly. Because diffusion is based on kinetic activity, anything that increases molecular activity quickens diffusion. Heating and mechanical agitation speed diffusion.
Temperature Scales
Fahrenheit, Celsius, Kelvin four key points are defined: (1) the zero point of each scale, (2) the freezing point of water (0°C), (3) body temperature (37°C), and (4) the boiling point of water (100°C).
laminar flow
Flows in parallel lines in a smooth progression Laminar flow is viewed as concentric layers of fluid flowing parallel to the tube wall at velocities that increase toward the center.
thermal conductivity
Heat transfer between objects is quantified by using a measure. centimeter-gram-second (cgs) solids (especially metals) tend to have high thermal conductivity. This is why metals feel cold
Convection
Heat transfer in both liquids and gases (fluids) involves the mixing of fluid molecules at different temperatures. the air is first warmed in one location and then circulated to carry the heat elsewhere; this is the principle behind forced- air heating in houses and convection heating in infant incubators. Fluid movements carrying heat energy are called convection currents.
Influence of pressure
High temperatures increase vaporization, whereas high pressures impede this process. Water molecules trying to escape from a liquid surface must push their way out against the opposing air molecules. If the surrounding air pres- sure is high, there are more opposing air molecules and vapor- ization decreases; alternatively, low atmospheric pressures increases vaporization.
kinetic energy
Kinetic energy is the energy of motion, such as that of a falling object. Most internal energy in gases is in the form of kinetic energy.
Evaporation
Liquid to gas In one form of vaporization, called evaporation, heat is taken from the air surrounding the liquid, cooling the air during strenuous exercise, the body takes advantage of this principle of evaporative cooling by producing sweat. The liquid sweat evaporates and cools the skin.
Properties of Liquids
Liquids exhibit flow and assume the shape of their container. Liquids also exert pressure, which varies with depth and density.
Clinical pressure measurements
Mercury is the most common fluid used in pressure measurements both in barometers and at the bedside. Because of the high density (13.6 g/cm3) of mercury, it assumes a height that is easy to read for most pres- sures in the clinical range. Water columns can also be used to measure pressure (in centimeters of water [cm H2O]), but only low pressures. Because water is 13.6 times less dense than mercury, 1 atm would support a water column 33.9 feet high or about as tall as a two-story building. Both mercury and water columns are still used in clinical practice, especially when vascular pressures are being measured. However, these traditional tools are rapidly being replaced by mechanical or electronic pressure-measuring devices. The simplest mechanical pressure gauge is the aneroid barometer, An aneroid barometer consists of a sealed evacuated metal box with a flexible, spring-supported top that responds to external pressure changes This same concept underlies the simple mechanical manometers used to measure blood or airway pressure at the bedside A flexible chamber can also be used to measure pressure electronically. These devices are called strain gauge pressure transducers. In these devices, pressure changes expand and contract a flexible metal diaphragm connected to electrical wires millimeters of mercury and centimeters of water are still the most common pressure units used at the bedside, they do not represent the SI standard. The SI unit of pressure is the kilopascal (kPa); 1 kPa equals approximately 10.2 cm H2O or 7.5 torr.
shear rate
The difference in the velocity among these concentric layers and is simply a measure of how easily these layers separate. Shear rate depends on two factors: (1) the pressure pushing or driving the fluid, called the shear stress, and (2) the viscosity of the fluid. Shear rate is directly proportional to shear stress and inversely proportional to viscosity. In uniform fluids such as water or oil, viscosity varies with temperature. Because higher temperatures weaken the cohesive forces between molecules, heating a uniform fluid reduces its viscosity. Conversely, cooling a fluid increases its viscosity. This is why a car's engine is so hard to start on a cold winter morning. The oil becomes so viscous that it impedes movement of the engine's parts. blood has a viscosity approximately five times greater than that of water. The heart works harder to pump blood than it would if it were pumping water. The heart must perform even more work when blood viscosity increases, as occurs in polycythemia (an increase in red blood cell concentration in the blood).
latent heat of fusion
The extra heat needed to change a solid to a liquid. The latent heat of fusion of ice is 80 cal/g, whereas the latent heat of fusion of oxygen is 3.3 cal/g.
Influence of surface area
The greater the available surface area of the gas in contact with air, the greater is the rate of liquid evaporation.
Partial Pressures (the Dalton's Law)
The pressure exerted by a gas mixture must equal the sum of the kinetic activity of all its component gases. The pressure exerted by a single gas in a mixture is called its partial pressure. Air is a good example of a gas mixture, consisting mainly of O2 and N2. The Dalton's law describes the relationship between the partial pressure and the total pressure in a gas mixture. Partial pressure = Fractional concentration × Total pressure A gas making up 25% of a mixture would exert 25% of the total pressure. For consistency, the percentage of a gas in a mixture is usually expressed in decimal form, using the term fractional concentration. A gas that is 25% of a mixture has a fractional concentration of 0.25. For example, air consists of approximately 21% O2 and 79% N. Assuming a normal atmospheric pressure of 760 torr, the individual partial pressure is computed as follows: PO2 =0.21× 760torr= 160torr PN = 0.79 × 760 torr = 600 torr
Pressure in Liquids
The pressure exerted by a liquid depends on both its height (depth) and weight density (weight per unit volume) PL =h×dw where PL is the static pressure exerted by the liquid, h is the height of the liquid column, and dw is the liquid's weight density.
melting point
The temperature at which a solid becomes a liquid. Ex: water (ice) has a melting point of 0°C, carbon has a melting point of greater than 3500°C, and helium has a melting point of less than −272°C. As the ice is heated, its temperature increases. At its melting point of 0°C, ice begins to change into liquid water.
Vaporization
Vaporization is the change of state from liquid to gas. Vaporization requires heat energy. large quantities of compressed and liquefied oxygen is kept in tanks; it is then exposed to ambient temperatures and vaporized into its gaseous form in order to be made available for patient use
buoyancy
Variations in liquid pressure within a container produce an upward supporting force, called buoyancy.
Viscosity
Viscosity is the force opposing a fluid's flow and is similar to friction in solids. The stronger these cohesive forces are, the greater the fluid's viscosity. The greater a fluid's viscosity, the greater its resistance to deformation and the greater its opposition to flow. The understanding of viscosity leads to the concept that fluids move in discrete cylindrical layers, called streamlines
Relative Humidity (RH)
When a gas is not fully saturated, its water vapor content can be expressed in relative terms using a measure RH(%) = content/Capacity × 100% For example, saturated air at a room temperature of 20°C has the capacity to hold 17.3 mg/L of water vapor (see Table 6.3). If the absolute humidity is 12 mg/L, the RH is calculated as follows: RH=12mg L 17.3mg L×100% = 0.69 × 100% = 69% When the water vapor content of a volume of gas equals its capacity, the RH is 100%. When the RH is 100%, a gas is fully saturated with water vapor. Under these conditions, even slight cooling of the gas causes its water vapor to turn back into the liquid state—a process called condensation. If air that is at an RH of 90% is cooled, its capacity to hold water vapor decreases. Although the water vapor capacity of the air decreases, its content remains constant. Rh air will increase Continued cooling decreases the air's water vapor capacity until it eventually equals the water vapor content (RH = 100%). When content equals capacity, the air is fully saturated and can hold no more water vapor. Because RH never exceeds 100%, any further decrease in temperature causes condensation.
Liquid-Solid Phase Changes (Melting and Freezing)
When a solid is heated, its molecular kinetic energy increases. If enough heat is applied, these vibrations eventually weaken the intermolecular attractive forces. At some point molecules break free of their rigid structure and the solid changes into a liquid.
Heat Transfer
When two objects exist at different temperatures, heat will move from the hotter object to the cooler object until both objects' temperatures are equal. Heat can be transferred in four ways: (1) conduction, (2) convection, (3) radiation, and (4) evapo- ration and condensation.
Gas Pressure
Whether free in the atmosphere, enclosed in a container, or dissolved in a liquid such as blood, all gases exert pressure tension is often used to refer to the pressure exerted by gases dissolved in liquids. gravity affects gas pressure. Gravity increases gas density, increasing the rate of molecular collisions and gas tension; this explains why atmospheric pressure decreases with altitude. Pressure is a measure of force per unit area. The SI unit of pressure is the N/m^2, or Pascal (Pa). Pressure in the cgs system is measured in dynes/cm^2, whereas pounds per square inch (lb/ in^2 or psi) is the British foot-pound-second (fps) pressure unit.
humidity deficit
a condition associated with a BH less than 100% that represents the amount of water vapor the body must add to the inspired gas to achieve saturation at body temperature (37°C).
Surface Tension
force per unit length (equivalent to surface energy density) exerted by like molecules at the surface of a liquid. For a given liquid, surface tension varies inversely with temperature: The higher the temperature, the lower is the surface tension. Surface tension plays an important role in determining the relative sizes of connected alveoli that if two alveoli of different sizes are con- nected, the smaller one will tend to empty into the larger one. However, this does not happen because, in reality, the two alveoli would have different surface tensions. because of the thin layer of surfactant inside the alveoli that counteracts the surface tension. As the radius of the alveoli decreases, its internal surface area also decreases but the volume of surfactant stays the same prematurity. These abnormali- ties may result in the collapse of alveoli secondary to high surface tension.
Properties of Gases
gases are readily compressed and expanded and fill the spaces available to them through diffusion. Diffusion; the process whereby molecules move from areas of high concentration to areas of lower concentration
Condensation
gases become liquids. vaporization takes heat from the air around a liquid (cooling), condensation must give heat back to the surroundings (warming).
Laws of Thermodynamics
laws describe how fundamental physical quantities (temperature, energy, and entropy) behave under various circumstances and forbid certain phenomena (such as perpetual motion). Work can be viewed as the process of transferring energy to or from a system. The increase in internal energy of a system can be observed as an increase in heat (as with a humidifier) or pressure (as during mechanical ventilation).
Freezing
liquid to solid. Opposite of melting. As the kinetic energy of a substance decreases, its molecules begin to regain the stable structure of a solid. the energy required to freeze a substance must equal that needed to melt it. The freezing and melting points of a substance are the same.
Melting
solid to liquid
Buoyancy (Archimedes Principle)
why certain objects float in water. The buoyant force (B) may be calculated as follows: B=dw ×V where dw is weight density (weight/unit volume) and V is volume of displaced fluid. If the weight density of an object is less than that of water (1 g/cm3), it will displace a weight of water greater than its own weight. In this case, the upward buoyant force will overcome gravity and the object will float. Conversely, if an object's weight density exceeds the weight of water, the object will sink. Gases also exert buoyant force, although much less than that provided by liquids. Buoyancy helps keep solid particles suspended in gases. These suspensions, called aerosols, play an important role in respiratory care.
