Lecture_01OCT

Lecture_01OCT - Quantitative relationships between reactants and products in chemical reactions STOICHIOMETRY Review Physical and chemical changes

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Unformatted text preview: Quantitative relationships between reactants and products in chemical reactions STOICHIOMETRY Review: Physical and chemical changes Matter can undergo two types of changes -- physical and chemical Physical changes are changes in the physical properties of a substance ( e.g., size, shape, density) or changes in the state of matter (solid, liquid, gas) without an accompanying change in chemical composition No new substances are formed in physical changes Examples : • Melting ice (change from solid to liquid state) • Boiling methanol (change from liquid to vapor state) • Heating water (increase in volume, decrease in density) • Hammering a gold nugget into a thin sheet of foil (change in size, shape) Matter can undergo two types of changes -- physical and chemical Chemical changes result in the formation of new substances that have different properties and composition than the starting materials Examples : • Adding vinegar to baking soda (Fzzing bubbles indicate acid-base neutralization reaction) • Heating a copper wire to form black residue on surface (conversion of metallic copper to copper oxide) • Using electricity to split water into hydrogen and oxygen gas (electrolysis) Review: Physical and chemical changes Review: Chemical equations In formal terms, a chemical change is referred to as a chemical reaction chemical equation -- shorthand for expressing a chemical reaction Example: Combustion of propane • propane and oxygen are consumed • carbon dioxide and water are produced • energy is released as light and heat propane + oxygen carbon dioxide + water C 3 H 8 ( g ) + O 2 ( g ) CO 2 ( g ) + H 2 O ( g ) Energy transitions associated with chemical reactions fall under the subject of thermodynamics (more on this later) Word equation Chemical equation A balanced chemical equation is an expression of the Law of Conservation of Mass Matter can not be created nor destroyed -- it can only shift from one form to another In a balanced chemical equation, the total number of atoms of each element must be the same on both sides of the equation-- you can think of this as applying accounting principles to chemistry In a chemical reaction, no atoms are created or destroyed-- they are just recombined to form new substances Review: Balanced chemical equations C 3 H 8 ( g ) + 5 O 2 ( g ) 3 CO 2 ( g ) + 4 H 2 O( g ) Equation: propane oxygen water carbon dioxide 3 carbon atoms,...
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This note was uploaded on 10/08/2010 for the course CHEM 1A taught by Professor Guay during the Fall '10 term at Laney College.

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Lecture_01OCT - Quantitative relationships between reactants and products in chemical reactions STOICHIOMETRY Review Physical and chemical changes

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