electrochemical series and galvanic cells

diff --git a/chem/electrochemistry.md b/chem/electrochemistry.md
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--- a/chem/electrochemistry.md
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@@ -1,16 +1,11 @@
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-header-includes:
-- \usepackage[version=4]{mhchem}
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-

 # Electrochemistry
 
 ## Oxidation states
 
 Indicates charge (ionisation) of an element
 
 # Electrochemistry
 
 ## Oxidation states
 
 Indicates charge (ionisation) of an element
 

-**Oxidation** - loss of e-  
-**Reduction** - gain of e-
+**Oxidation** - loss of e- (at anode)  
+**Reduction** - gain of e- (at cathode)

 
 Main group elements (i.e. group 2) - generally one oxidation state:
 
 
 Main group elements (i.e. group 2) - generally one oxidation state:
 


@@ -26,15 +21,14 @@ Main group elements (i.e. group 2) - generally one oxidation state:
 
 Transition metals (d shell) may have several oxidation states.
 
 
 Transition metals (d shell) may have several oxidation states.
 

-$$\ce{H_2}$$
-

 Common oxidation numbers:
 
 Common oxidation numbers:
 

-| elements          | common ox. no. in compounds | exceptions          |
-| ----------------- | --------------------------- | ------------------- |
-| main group metals | valency                     | no                  |
-| hydrogen          | +1                          | metal hydrides (-1) |
-| oxygen            | -2                          |
+| elements          | common ox. state | exceptions          |
+| ----------------- | ---------------- | ------------------- |
+| main group metals | valency          |                     |
+| hydrogen          | +1               | metal hydrides (-1) |
+| oxygen            | -2               | ce{H2O2} (-1)       |
+| halogens          | -1               |                     |

 
 
 ### Rules for oxidation states
 
 
 ### Rules for oxidation states


@@ -44,3 +38,29 @@ Common oxidation numbers:
 - oxidation number of simple ion is the charge of the ion
 - sum of oxidation numbers in polyatomic ion is the charge of the ion
 - sum of oxidation numbers of a neutral compound is zero
 - oxidation number of simple ion is the charge of the ion
 - sum of oxidation numbers in polyatomic ion is the charge of the ion
 - sum of oxidation numbers of a neutral compound is zero

+
+## Electrochemical series
+
+- Top is most likely to be reduced
+- Strongest reductants are bottom right
+- Strongest oxidants are top left
+- Strong oxidants have weak conjugate reductants
+- $E^0$ values are measured relative to ce{H2} / ce{H^+} = 0V
+
+## Conjugate redox pairs
+
+Oxidant and conjugate *reduced form*  
+e.g. ce{Cu^2+} / ce{Cu}, $\quad$ ce{Zn^2+} / ce{Zn}
+
+Usually one member of pair is used as electrode (except for *inert electrodes*, e.g. platinum)
+
+## Electrochemical/galvanic cells
+
+1. Find two half reactions involved (between electrode and solution)
+2. Higher equation will proceed left to right
+3. Lower equation will proceed right to left
+
+emf for each cell is calculated as $E^0(\text{red}) - E^0(\text{ox})$  
+Then total emf is $\sum_{i=1}^2 \Sigma E^0({i})$
+
+For a spontaneous reaction to occur, species on left must be in electrical contact with species on lower right
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