Chapter 11

# Chapter 11 - Chapter 11 : States of matter - liquids and...

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Chapter 11 : States of matter - liquids and solids we have talked about the property of gases and laws that describe their behavior, now move on to liquids and solids CO2(s) ----> CO2(g) at -78 C and 1 atm pressure whereas H2O(s) ----> H2O(l) ----> H2O(g) 0 C, 100 C, 1 atm these changes in state are called phase transitions why does carbon dioxide go directly from a solid to a gas without passing first through a liquid state like water does? can force CO2 gas to liquefy by increasing the pressure to over 5 atm and cooling substances can change physical state from solid to liquid to gas and vice versa depending on temperature and pressure - we would like to understand how these parameters contribute to determine the state of a molecule (why is CO2 a gas when H2O is a liquid, why is mercury a liquid when iron is a solid) why is solid ice less dense than liquid water? ice cube float in the top of a glass, ponds and lakes freeze at the top, not at the bottom - why is this important? cycle of life depends on this!!! remember that gases are compressible fluids, they can be compressed to smaller volumes by increasing the pressure on them forcing the molecules into a smaller space - this is possible because most of the volume of a gas is empty space, very little is the actual molecules in contrast, liquids are relatively incompressible - cannot easily force a liquid into a smaller volums like a gas - molecules do move in a liquid according to kinetic-molecular theory in constant random motion like a gas, but molecules are more closely packed together, so there is less available space to compress the molecules into, unlike a gas

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solids are essentially incompressible and are not fluids - molecules do not move freely, like in a gas or liquid, but are relatively fixed in space and only move very slightly around specific points - oscillate or vibrate Figure 11.2 again remember, the molecules in a gas nearly obey the ideal gas law PV =nRT because there is very little interaction between molecules in the gas and because the volume occupied by the gas molecules themselves is nearly negligible - the van der Waals equation (P + n2a2/V2)(V - nb) = nRT was one attempt to correct for this, but could still relate T, V, and P fairly well cannot do this for liquids and solids - cannot neglect the volume occupied by the molecules relative to the total volume and cannot neglect the forces of interaction between the molecules, when they are actually very important when you discuss the behavior of liquids and solids phase transitions: H2O(s) ---> H2O(l) melting, fusion ice->water H2O(l) ---> H2O(g) vaporization water->steam H2O(l) ---> H2O(s) freezing water->ice H2O(s) ---> H2O(g) sublimation ice->water vapor H2O(g) ---> H2O(l) condensation water vapor-> water (dew) H2O(g) ---> H2O(s) condensation water vapor-> frost some of the molecules in all liquids and even some solids are slowly turning to the vapor phase - if you put a liquid into a sealed vessel, some of the liquid will
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## Chapter 11 - Chapter 11 : States of matter - liquids and...

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