Solids Liquids Gases Phase Transition

# Solids Liquids Gases Phase Transition - Week 2 Bulk...

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Week 2 Bulk Properties of Gases, Liquids, and Solids: Molecular Interpretation Molar Volume: o Liquids and Solids generally take up much less volume per mole than Gases. 24L/mol for an ideal gas. Upon melting, most solids change in volume by only 2-10% Therefore, we can say that the distance between molecules in liquids and solids is not much Intermolecular connections in solids and liquids are much smaller in solids and liquids than in gases. Compressibility o Fractional decrease in volume as applied pressure is increased. o Gases are highly compressible whereas solids and liquids are not Why? Only modest energy is required to bring the widely separated gas molecules closes together, because forces between them are negligible. However, for solids and liquids, there are strong repulsion forces (electrons in the electron clouds) which prevent this. Thermal Expansion o Coefficient of Thermal Expansion: fractional increase in the volume of a substance per degree increase in temperature. o Solids and Liquids have low coefficients, whereas gases have high coefficients. Why? The strong intermolecular forces have to be overcome by the energy added in order to expand. This is easier in gases that have negligible intermolecular forces than in gases. Fluidity and Rigidity o Fluidity: property of liquids and gases o Rigidity: property of solids o Viscosity: ease of flow Maple syrup has high viscosity, whereas water has low viscosity o Hardness: resistance to indentation o Elasticity: capacity to recover shape when a deforming stress is removed Diffusion: o When two substances are placed next to each other and start to mix Think osmosis or ion gradients in cells that diffuse through cell membranes o Gases: at room temperatures, they diffuse at rates in cm/s. o Diffusion constant: rate of diffusion Surface Tension: o Surface of a liquid resists attempts to increase its area against a gas o Behaves like a “skin” on top of the liquid

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Think about when you fill water in a glass a little too high…it doesn’t spill right away, it forms a “dome” on top of the glass. That “dome” is the water resisting the increase in volume. o
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Solids Liquids Gases Phase Transition - Week 2 Bulk...

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