R 2.1 - 2.2
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What is the law of conservation of mass and its effects?
Mass cannot be created or destroyed but can be transformed from one form into another, so equations must be balanced
Why are state symbols important in writing the reaction?
they can affect the outcome of a chemical reaction and the rate of a reaction some reactions can only occur in certain states, like aqueous
What are molar ratios and where are they shown?
ratio of reactants and products in a reaction, shown in a chemical equation
3 different equations for number of moles in different states
n = CV (for aqueous solutions) n = mass/Mr (for solids) n = V/molar volume (for gases)
What are the excess and limiting reactants?
limiting: reactant which is always fully used up and determines the yield of the product, since there is less of it excess: reactant which is still remaining after the reaction occurs, since there is more of it
What is the theoretical yield?
maximum amount of product that could be obtained from a chemical reaction, assuming that the reaction is fully carried out under ideal conditions
What are some factors that can cause there to be less product than expected in an experiment?
• loss of product, through evaporation, spillage, isolation, or purification • incomplete reaction, due to impurities or lack of time • alternative reactions, could bring different products • impurities in one or more reactants
What are some factors that can cause there to be more product than expected in an experiment?
• impurities present in the product (eg moisture/solvent in the incomplete drying of a precipitate/solid product) • product undergoes subsequent reactions with surroundings
What is the percentage yield =?
experimental yield/theoretical yield*100
What is the experimental yield?
how much product is actually obtained
Definition of percentage yield
a measure of the amount of product obtained compared to what should have been obtained, measures efficiency
What are two ways that the efficiency of a reaction can be measured?
• percentage yield • atom economy
What is the atom economy?
a measure of a reaction’s efficiency regarding the total mass of reactant atoms which end up as desired products (not by-products), as a %
atom economy =
molar mass of desired products/molar mass of all reactants*100
Relationship between atom economy and the amount of waste produced
inverse - as waste increases, atom economy decreases
What is inverse proportionality?
as one variable increases, the other decreases and vice versa
What do high/low atom economies suggest?
high - reaction was efficient at using up all the reactants + producing minimal waste low - some of the reactants weren’t used effectively, unwanted by-products were formed instead, high amount of waste
Why is atom economy important?
industry, deciding how to produce a certain substance
What is Green Chemistry and what is an important aspect of it?
field of science focused on chemical processes/products that are eco-friendly atom economy is important - reduced amount of waste, simpler reactions, more efficiency
What is the rate of reaction?
change in concentration of products/reactants per unit time
What happens to concentrations during reactions?
reactant conc. decreases and product conc. increases
What is the difference in rates for formation of products/usage of reactants?
change in reactants - negative rate change in products - positive rate
What are the main ways to measure rates of reaction?
• measuring change in volume of a gas • measuring changes in mass • measuring changes in colour • measuring changes in conductivity • measuring rate of precipitate formation • measuring the rate of clock reactions
Explain how to measure change in volume of a gas.
• usually done with a gas syringe connected to a bung and delivery tube • gas pushes syringe out