Week 3 Flashcards
Rules of balancing chemical equations
- write your unbalanced equation
- change only coefficient, don’t touch subscripts
- count number of atoms that appear on each side
- begin with elements that appear only in one product and reactant
- balance most metallic elements first
- leave hydrogen and then oxygen until last
- ensure coefficients are in lowest possible ratio
What are chemical reactions?
Involve charge with atoms, molecules or ions rearranging to form new substances. In the process, chemical bonds are broken and new bonds are formed.
Components of writing down a chemical reaction
- reactants
- state of material
- arrow (yields)
- process applied (above arrow)
- products
Reactants
Substances that are changed in a chemical reaction
Products (of a reaction)
Substances created as a result of a chemical reaction
Steps to write a chemical equation
- identify starting materials
- indicate proportions (stoichiometry) in which they are present
- indicate any products formed
Steps to doing calculations involving chemical reactions
- write a balanced equation for the reaction
- convert all masses to moles to allow direct comparison of species in chemical reaction
- compare stoichiometry in equation to the moles calculated and determine the limiting reagent
- determine products formed
- convert product moles back to mass to express final answer
Why must we calculate yields?
Chemical reactions rarely go to completion and stoichiometric equations show the optimum case in the conversion of reactants to products (100%)
% yield
% yield =the actual product yield/maximum possible yield x 100
Alkali metals and water
Group 1 metals react with water to produce a basic solution (a hydroxide) and hydrogen. Violent and exothermic reaction.
General alkali metal and water reactions
2M(s) + 2H20 —-> 2MOH(aq) + H2(g)
Combustion of hydrocarbons
- hydrocarbons (compounds containing carbon and hydrogen) burn in excess oxygen to produce carbon dioxide and water
Combustion of hydrocarbons general reaction
R + O2(g) —> CO2(g) + H2O(l)
Acid base reactions
Acidic compounds will react with a base to produce a salt and a water
Acid + base —> salt + water
Acid carbonate reactions
Acidic and hydrogen carbonate and carbonate salts combine to produce a salt, carbon dioxide and water
General acid carbonate reactions
2HA + M2CO3 —> 2MA + CO2(g) + H2O(l)
