PDP Chemistry Chemical reactions Topic 1: Chemical reactions • • • • • • • Atoms Chemical reactions are atoms rearranging Equations Signs of a chemical reaction Balancing chemical equations Types of chemical reaction Measuring chemical quantities How are you going to take notes? Atoms What is everything made of? In Six Easy Pieces, Richard Feynman said: If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis that all things are made of atoms. (Almost) everything is made of atoms Images:http://en.wikipedia.org/wiki/Rock_(geology), http://en.wikipedia.org/wiki/Tree , http://en.wikipedia.org/wiki/Human, http://en.wikipedia.org/wiki/Star How big is an atom? about 10-10m if an atom was the size of a grain of sand, humans would be the size of a planet. Image: http://en.wikipedia.org/wiki/Earth, http://en.wikipedia.org/wiki/Sand The periodic table lists the elements in order of atomic number Image: http://en.wikipedia.org/wiki/File:Periodic_table.svg Chemistry is atoms rearranging Describing chemical changes Liquid oxygen and liquid hydrogen fuel Launch of Apollo 11 (from 6 min) Image: http://en.wikipedia.org/wiki/Saturn_V Some changes are only changes of phase, not chemical changes Image: https://commons.wikimedia.org/wiki/Categor y:States_of_aggregation Atoms are rearranged to make new substances in chemical reactions. Hydrogen + Oxygen Water 2 H2 + O2 2 H2O Image: http://labspace.open.ac.uk/mod/resource/view.php?id=438900 Equations describe chemical reactions reactants products Hydrogen + Oxygen Water 2 H2 + O2 2 H2O State symbols (s) (l) (g) (aq) Signs of a chemical change How do we know a chemical reaction is occurring? Sodium reacts with water Dilute sulphuric acid reacts with potassium hydroxide solution Lead nitrate solution reacts with potassium iodide solution Magnesium and hydrochloric acid Signs of a chemical change Elements, compounds, atoms, molecules, ions Molecules Build a molecule PhET http://phet.colorado.edu/en/simulation/build-a-molecule States of matter: Basics http://phet.colorado.edu/en/simulation/states-of-matterbasics What is an atom? Symbols and formulae Ethane, C2H6 Naming compounds Ionic compounds (usually metal + non-metal) NaCl KI LiF CaCl2 MgSO4 CaCO3 H2SO4 H2O Common Cations Common Name Formula Alternative name Simple Cations Aluminium Al3+ Calcium Ca2+ Copper(II) Cu2+ cupric Hydrogen H+ Iron(II) Fe2+ ferrous Iron(III) Fe3+ ferric Magnesium Mg2+ Mercury(II) Hg2+ mercuric Potassium K+ kalic Silver Ag+ Sodium Na+ natric Polyatomic Cations Ammonium NH4+ Hydronium H3O+ Common Anions Common Name Formula Simple Anions Chloride Cl− Fluoride F− Bromide Br− Oxide O2− Polyatomic anions Carbonate CO32Hydrogen HCO3− carbonate Hydroxide OH− Nitrate NO32Phosphate PO43Sulfate SO42Anions from Organic Acids Ethanoate CH3COO− Methanoate HCOO− Ethandioate C2O4−2 Cyanide CN- Alternative name bicarbonate acetate formate oxalate Covalent compounds (usually non-metals) CO2 H2O CO NH3 SO2 SO3 CH4 Equations for lab Balancing chemical equations Balanced equations show the mole ratio of reactants and products Hydrogen + Oxygen Water 2 H2 + O2 2 H2O Image: http://labspace.open.ac.uk/mod/resource/view.php?id=438900 2 H2 + O2 2 H2O green numbers = subscripts cannot be changed (a compound has one formulachanging the formula changes the compound) red numbers = coefficients changes to balance the reaction (coefficients valid only for a specific reaction) Balancing a chemical equation Propane + oxygen carbon dioxide + water _ C3H8(g) + _ O2(g) _ CO2(g) + _ H2O(l) C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(l) What does an equation tell us about molecules in the reaction? you need 5 oxygen molecules for 1 molecule of propane 1 propane molecule will produce 3 carbon dioxide molecules and 4 Water molecules 2 molecules of propane produce 6 molecules of carbon dioxide 1 mole of propane produces 3 moles of carbon dioxide Measuring chemical quantities Measuring chemical quantities: solids in grams using a balance (precision ±0.01g or ±0.001g) Image: http://en.wikipedia.org/wiki/Weighing_scale Measuring chemical quantities: liquids in litres (L) or decimetres cubed (dm3) 1L = 1dm3 In mL or centimetres cubed (cm3) 1mL = 1cm3 1000 mL = 1L Images: http://commons.wikimedia.org/wiki/Category:Laboratory_glassware Converting mass to volume volume = mass x density volume of pure water is 1.0 gcm-3 Solutions a solute dissolved in a solvent gives a solution units of concentration grams per litre (gL-1) or moles per decimetre cubed (moldm-3, M) Types of chemical reaction -synthesis -decomposition -displacement -double displacement (special type acid-base) -combustion Links Powers of ten http://www.powersof10.com/ hydrogen explosion http://www.youtube.com/watch?v=DjcztiNGg_8 states of matter phet http://phet.colorado.edu/en/simulation/states-of-matter