PHYSICAL CHEM - REDOX REACTIONS
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What is reduction?
• loss of O2 • gain of electrons
What is oxidation?
• gain of O2 • loss of electrons
What does a reducing agent do?
donates electrons
What does an oxidising agent do?
accepts electrons
What is the oxidation state of an atom?
the total no. of electrons that an atom has donated/accepted
What are the rules for working out oxidation states?
• uncombined elements have an oxidation state of 0 • elements only bonded to identical atoms (eg: O2) have an oxidation state of 0 • the oxidation state of a monatomic ion (eg: Na^+) is the same as its charge • in compound ions the overall oxidation state is its charge • sum of oxidation states for neutral compounds is 0 • combined O’s oxidation state is nearly always -2 (except for in peroxides) • combined H’s oxidation state is almost always +1 (except for in metal hydrides where its -1)
What are the steps of writing a half equation?
• calculate oxidation states on each side of the equation • balance the element changing oxidation state • sort out electrons (if oxidation state becomes more -ve it gains electrons, if it becomes more +ve it loses electrons) • sort out Os (for every O gained/lost add/remove 1 H2O molecule) • sort out Hs (for every H gained/lost add/remove 1 H^+ ion) • check if total charge on the left = the total charge on the right
How do you combine half equations?
• add them together • cancel out electrons • cancel out any H^+ and/or H2Os