Answer to Question #305839 in General Chemistry for wtjr

Question

the mass of Cu2Se formed when 40.0g copper metal reacts with 28.0g selenium

Answer 1

• Step 1: Write a balanced equation
• 2Cu + Se ----> Cu₂Se
• Step 2: Find the moles of copper and selenium in their masses.
• 64g of copper is in 1 mole, what about 40g
• 40/64 = 0.625moles of copper.
• 79g of selenium is in 1 mole, what about 28g
• 28/70 = 0.4 moles of selenium.
• Finally, find the excess reactant by using mole ratio.
• Mole ratio copper: selenium is 2:1
• 0.625/2=0.3125 moles of copper vs 0.4 moles of selenium.
• You realize that selenium is in excess.
• Therefore, we will use the limiting reactant which is copper and mole ratio to get the mass of Cu₂Se
• 0.625moles are rati0 2 what about ratio 1
• 0.625/2 = 0.3125 moles.
• You can convert this to mass by multiplying with molar mass of Cu₂Se
• 0.3125 x 206 = 64.375g of Cu₂Se