1. Stoichiometric Relationships
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What is kinetic energy?
Energy related to motion of an object
Solid, liquid, gas: Arrangement
Solid: Closely packed Liquid: Also close together but less then solid Gas: Most spread out, far apart
Solid, liquid, gas: Intermolecular forces
Solid: Strongest forces Liquid: Weaker forces Gas: Negligible forces
Solid, liquid, gas: Motion
Solid: Vibrate at fixed positions Liquid: Slide past each other Gases: Move randomly
Solid, liquid, gas: Shape
Solid: Fixed shape Liquid: No fixed shape, takes shape of container Gas: No fixed shape
Solid, liquid, gas: Volume
Solid: Fixed volume Liquid: Fixed volume Gas: No fixed volume
What are all the changes of state?
• Solid to liquid: Melting • Liquid to gas: Evaporation • Gas to liquid: Condensation • Liquid to solid: Freezing • Solid to gas: Sublimation
What is opposite of sublimation?
Deposition (gas to solid)
Why does change of state occur?
An increase in temperature = increase in average kinetic energy of molecules which allows them to overcome intermolecular forces and hence build or break bonds
Examples of sublimation
Iodine, CO2, NHCl, Mothballs, Dry ice
Difference between evaporation and boiling
• Evaporation takes place at surface and below boiling point, happens at range of temperatures • Boiling has a specific temperature and occurs throughout the liquid
What does flat part on heating or cooling curve show and why?
It shows the melting or boiling points because when there is a change of state, the temperature remains constant
Density
Mass per unit volume (D= m/v)
Unit for density
g/cm^3 or kg/m^3
Element
Something that is made of the same kind of atom
Compound
Chemically combined substance of 2 or more different elements
Are H2 and O2 compounds?
No. They are molecules
Differences between elements and compounds
• Elements are made of one type of atom • Elements cannot be further broken down while compounds can be chemically • Elements are represented by a symbol instead of formulae • Element’s properties are determined by valence electrons while compound’s properties differ from their constituent elements • 118 known elements while compounds have endless possibilities
Mixture
2 or more substances that are not chemically combined
Difference between mixtures and compounds
• Compounds are chemically combined while mixtures are physically • Compounds are in fixed ratio • Compounds are pure • Compounds have a formulae • Properties of compounds differ but mixtures retain properties of their elements/substances
Difference between homogenous and heterogenous mixture
• Homogenous have uniform dispersion • Homogenous have fixed ratio/composition • Heterogenous are immiscible while homogenous do not physically separate on standing
Examples of homo and heterogenous mixtures
Homogenous: Air, honey Heterogenous: Sand + water, oil + water
Are solutions homo or heterogenous?
Homogenous
Solute
Substance that is DISSOLVED