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Chemical Reactions. New Substances produced by changing the way atoms are arranged Physical Changes ≠ Chemical Reaction Evidence Change in Color (rust) Temperature Change (endo/exo-thermic) Formation of a Gas Formation of a Solid (Precipitate).
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Chemical Reactions • New Substances produced by changing the way atoms are arranged • Physical Changes ≠ Chemical Reaction • Evidence • Change in Color (rust) • Temperature Change (endo/exo-thermic) • Formation of a Gas • Formation of a Solid (Precipitate)
Reactants: Substances Present @ Beginning • Products: Substances Formed by the Reaction • Yields: An “equal sign” in a chemical reaction meaning “produces”, “creates”, or “forms”… Na + Cl2 NaCl Reactants Yields Products Product Reactants
Synthesis …Combining Elements… A + B AB Mg + O2 MgO Product Reactants
Decomposition …Separating Elements… CD C + D H20 H2 + O2 Reactants Product
Combustion …FIRE! (Needs Oxygen and produces CO2 )… EF + O2 H20 + CO2 + HEAT CH4 + O2 H20 + CO2 Reactants Product
Single Replacement …Switch out ONE element with another!... GH + I GI + H CuCl2 + Zn ZnCl2 + Cu Reactants Product
Double Replacement …Switch Out Two Elements with Two Others!... JK + LM JM + KL AgNO3 + HCl AgCl + HNO3 (Stop Here) Reactants Product
Rate of Reaction • Concentration • High Concentration = faster reaction • The more particles – the more chance of collisions • Surface Area • More surfaces available to react = faster reaction • Temperature • Higher Temperatures = faster reaction • Particles speed up or slow down…speeding up or slowing down the reaction…
Rate of Reaction (Cont’d) • Catalyst • Something that speeds up the rate of reaction without being affected itself. • A good example is the way the platinum catalyst in a car’s catalytic converter works to change toxic carbon monoxide into less-toxic carbon dioxide. • Inhibitor • Something that slows down the rate of reaction without being affected itself.
The Law of Conservation of Mass • Matter Can Neither Be Created Nor Destroyed • Reactants and Products MUST be EQUAL!
Endothermic Reactions • Endothermic reactions are reactions which take energy in from their surroundings. • If a substance is undergoing an endothermic reaction would it’s surroundings get warmer or colder? • It’s surroundings get colder. • Endothermic reactions occur when the bonds of a substance are being broken.
Useful Endothermic Reactions • When things dissolve they are undergoing an endothermic reaction. • Cooking is an endothermic reaction. • The food takes in the heat provided by the cooker. • The chemicals of the food undergo a chemical reaction which makes them easier to digest. • Cold packs for sports injuries rely on endothermic reactions. • When you twist or shake the pack the chemicals in the pack start reacting. • Because they undergo an endothermic reaction they take heat in from their surroundings. • This makes the pack cold.
Exothermic Reactions • Exothermic reactions give off heat. • They occur when chemical bonds are formed. • If substances are undergoing exothermic reactions will their surroundings get hotter or colder? • The will get hotter.
Useful Exothermic Reactions • Combustion: all combustion reactions give off heat. • Neutralization reactions are exothermic. • Hot Pad hand warmers • When the hand warmer is shaken they chemicals inside undergo an exothermic reaction • This releases the heat which helps to warm up your hand.