double+displacement+reactions.+(teaching+wiki..)


 * DOUBLE DISPLACEMENT REACTIONS**

//what happens:// a double displacement reaction is a bit like single displacement, only more complicated. in a double displacement reaction, two compounds react and yield two new compounds. the cations of the reactant compounds (the first element in the compound) switch places in the new compounds. //generic form of a double displacement reaction:// a simple generic form of a double displacement reaction is AB + CD --> AD + CB.

EXAMPLE EQUATION //equation in sentence form:// __potassium iodide and lead(II) nitrate react to produce lead(II) iodide and potassium nitrate__.

//change into formula equation:// potassium iodide was used in an aforementioned synthesis example reaction, it was mentioned that in a chemical formula form it is KI, potassium (K) and iodine (I). lead(II) nitrate was also previously used in a single displacement example reaction, from that example, it is known that the correct formula is Pb(NO3)2, lead (Pb) and nitrate (NO3). lead(II) iodide is PbI, lead (Pb) and iodine (I), but not fully balanced. potassium nitrate is unbalanced as KNO3, potassium (K) and nitrate (NO3). the equation; KI + Pb(NO3)2 --> PbI + KNO3, now needs to be balanced. //balancing the equation:// first, the charges of each compound need to be balanced out. KI and KNO3 already has a balanced charge, as does the given Pb(NO3)2. but lead(II) iodide is not. because it is lead(II), lead has a +2 charge, iodine has a -1 charge, so there need to be two iodines. the formula then becomes PbI2. now the full equation must be balanced; KI + Pb(NO3)2 --> PbI2 + KNO3. there is only one I on the reactant side, and two on the product side, so the reactant side needs a coefficient of 2. this makes two K's on the reactant side, a coefficient of 2 needs to be placed with the single K on the product side. the makes two nitrates on the product side, when there are already two on the reactant side. there is one Pb on both sides. 2KI + Pb(NO3)2 --> PbI2 + 2KNO3 is now fully balanced.



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