Chapter 8 lecture notes PDF

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lecture notes for chapter 8...

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Chapter 8 Quantities in Chemical Reactions Stoichiometry - the study of the numerical relationships between chemical quantities of reactants and products in the chemical reaction. - Everything is consumed in the reaction as written down in the form of a balanced chemical equation Mass of a Compound Produced or Consumed in a Reaction - 2 conversion factors needed: - Molar mass is one conversion factor. - Molar ratio from a balanced equation is another. Theoretical vs Actual Yields - The amount of product calculated from the equation (taking into account limiting reagent) is the theoretical yield. - When you run a reaction, the amount of product collected is the actual yield. - These may not be the same because a fraction of the product may spill, escape as gas, stay deposited on the walls of the test tubes etc. - There is also such thing as human error ... - The percent yield is the amount of the actual yield compared to the theoretical yield. - actual/theoretical x 100% = percent yield Enthalpy of a Reaction - In a chemical reaction, energy is gained or lost. - Products may contain less or more energy than reactants. - Energy produced or consumed in the reaction is called the enthalpy of reaction: ΔHrxn. - Exothermic - heat released to surrounding - Endothermic - heat absorbed from surroundings Exothermic Process - A type of reusable instant HOT packs produces heat by crystallization of sodium acetate. - Precipitation is initiated by compressing a metal disk within the pouch of supersaturated NaCH3COO solution. The process is exothermic and the pouch warms up as the salt crystallizes. Enthalpy and Chemical Equation - Enthalpy of reaction (ΔHrxn) follows molar ratios of the balanced equation and is listed to the right of the equation. - Combustion of iron metal is an exothermic reaction that releases 1652 kJ of heat per mole of balanced reaction: - Energy is produced by the reaction, so the sign for the enthalpy is negative....