Phases or states of matterGASESThe particles in a gas move rapidly and randomlyThe kinetic energy of the particles is very high and all order hasbeen lost.The particles are far apart and so also have high potential energyGases are either covalently bonded molecular substances withweak intermolecular forces (small molecules with few electrons)or atomic substances like thenoblegases.To simplify the study of gases we assume that the particles:·are moving randomlydonotattracteachotherhavenovolumeandhaveelasticcollisions11
11 Phases or states of matter The particles in a gas move rapidly and randomly. The kinetic energy of the particles is very high and all order has been lost. The particles are far apart and so also have high potential energy. Gases are either covalently bonded molecular substances with weak intermolecular forces (small molecules with few electrons) or atomic substances like the noble gases. To simplify the study of gases we assume that the particles: ● are moving randomly ● do not attract each other ● have no volume ● and have elastic collisions GASES
Phases or states of matterThese assumptions are known as the postulates ofthekinetictheory and a gas in which the particles behave like this is calledan ideal gas. In such a gas the kinetic energy of the particles is ameasure of their temperature.For an ideal gas the equation:PV= nRT can be appliedReal gases approach ideal behavior when the pressure is very low(the particles are far apart and do not attract each other) and/orwhen the temperature is very high (the particles are moving veryfast and not near each other).Conversely, gases are least ideal at high pressure and lowtemperature.12
12 Phases or states of matter These assumptions are known as the postulates of the kinetic theory and a gas in which the particles behave like this is called an ideal gas. In such a gas the kinetic energy of the particles is a measure of their temperature. For an ideal gas the equation: PV = nRT can be applied Real gases approach ideal behavior when the pressure is very low (the particles are far apart and do not attract each other ) and/or when the temperature is very high (the particles are moving very fast and not near each other). Conversely, gases are least ideal at high pressure and low temperature
Phasesor statesofmatterWordsWordscondense;freezedisrupt: cause disorder in (sth).Raoult'slawideal gas;idealliquidrandomly:randompostulate nconversely13
13 Phases or states of matter Words Words condense; freeze disrupt: cause disorder in (sth). Raoult’s law ideal gas; ideal liquid randomly: random postulate v n conversely
PhaseequilibriaPhase eguilibria:The behavior of substances as they change statePHASEDIAGRAMThis shows the conditions under which the different phases orstates of apure substanceexistGAS(VAPOUR)SOLIDLIQUID1atmospherepressureboilingpointfreezingpointtemperature14
14 Phase equilibria The behavior of substances as they change state This shows the conditions under which the different phases or states of a pure substance exist Phase equilibria: PHASE DIAGRAM
Phase equilibriaThe magnifiedportion of the curves, drawn above, shows howthe saturated vapor pressure, often just called the vapor pressure,of a pure liquid changes with temperature.HotliquldhighvapourpressurepressureColdliquid=lowvapourpressuretemperature
15 Phase equilibria The magnified portion of the curves, drawn above, shows how the saturated vapor pressure, often just called the vapor pressure, of a pure liquid changes with temperature