F4.2 moles of copper metal react with 6.3 moles of silver nitrate, how many moles of silver metal can be formed, and how many moles of the excess reactant will be left over when the reaction is complete? unbalanced equation: cu + agno3 → cu(no3)2 + ag

1. Balance the reaction
Cu + 2AgNO3 → Cu(NO3)2 + 2Ag 
2. Find the limiting [divide moles of reactant by their balancing numbers]
Cu: 4.2/1 =4.2 
AgNO3: 6.3/2= 3.15 
AGNO3 is the limiting
How many moles of silver metal will be formed?
The ratio between the limiting reactant and silver is 2:2 or 1:1
therefore 6.3 moles of silver will be formed.

How many moles of excess reactant will be left?
Since each mole of copper is equal to 2 moles of AgNO3. divide 6.3 by 2 then minus it from coppers moles
6.3/2 = 3.15
4.2-3.15 = 1.05 moles of copper will be left

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.