Answer:
moles of Cu° needed = ½ (5.8 moles) = 2.9 moles Cu° needed.
Explanation:
Cu + 2AgNO₃ => Cu(NO₃)₂ + 2Ag
? moles Cu + 5.8 moles AgNO₃ => Cu(NO₃)₂ + 2Ag
Note coefficient of Cu° vs coefficient of AgNO₃
=> 1 mole Cu° < 2 moles AgNO₃ ...
=> Since moles of Cu° are smaller than moles of AgNO₃ in the given equation, the moles of Cu° needed to react with 5.8 moles AgNO₃ will be smaller than the 5.8 by the ratio of coefficients that will make 5.8 smaller. That is ...
moles of Cu° needed = ½ (5.8 moles) = 2.9 moles Cu° needed.
Note: Using 2/1(5.8) will make value greater than 5.8 and incorrect.
One can also set up a ratio relationship as follows...
1 mole Cu° <=> 2 moles AgNO₃ (fm equation)
? mole Cu° <=> 5.8 moles AgNO₃ (problem)
=> (1 mole Cu°)/X=(2 mole AgNO₃)/(5.8 moles AgNO₃)
=> X = (1 mole Cu°)(5.8 mole AgNO₃)/2 mole AgNO₃
= ½(5.8) mole Cu° = 2.9 mole Cu°
