# equations and calculations

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• equations and calculations
• ideal gas equation
• pV=nRT
• R=8.31J/K/mol
• p=pressure (Pa)
• V=volume (m3)
• n=mole
• T=temperature (K)
• K=celcius +273
• calculates number of moles in a certain volume of gas
• percentage yield
• never 100%
• %yield=(actual yield/theoretical yield)x100
• reasons for actual yield being less than theoretical yield.
• incomplete reactions
• some chemicals are lost e.g. left on filter paper
• atom economy
• the measure of the efficiency of a reaction
• (mass of desired products/ total mass of reactants or products) x100
• companies try to use reactions with high atom economies because:
• better for the environment due to less waste
• more efficient use of raw materials and so more sustainable
• less expensive
• molecular and empirical formula
• empirical formula is the simplest whole number ratio of atoms
• 1. find moles in 100g of atom = abundance /Ar
• 2. divide each number of moles by the mallets number of moles
• molecular formula is the actual whole number ratio of atoms