Because the copper roofs, have been outside for a while and oxidization has occurred.
When metals become oxidized they rust, but when copper becomes oxidized, it turns greenish.
So copper roofs oxidize and turn green from being outside and a copper square doesn’t if it’s inside.
<u>Given:</u>
Mass of Ag = 1.67 g
Mass of Cl = 2.21 g
Heat evolved = 1.96 kJ
<u>To determine:</u>
The enthalpy of formation of AgCl(s)
<u>Explanation:</u>
The reaction is:
2Ag(s) + Cl2(g) → 2AgCl(s)
Calculate the moles of Ag and Cl from the given masses
Atomic mass of Ag = 108 g/mol
# moles of Ag = 1.67/108 = 0.0155 moles
Atomic mass of Cl = 35 g/mol
# moles of Cl = 2.21/35 = 0.0631 moles
Since moles of Ag << moles of Cl, silver is the limiting reagent.
Based on reaction stoichiometry: # moles of AgCl formed = 0.0155 moles
Enthalpy of formation of AgCl = 1.96 kJ/0.0155 moles = 126.5 kJ/mol
Ans: Formation enthalpy = 126.5 kJ/mol
The balanced neutralization reaction here is:
Ca(OH)2 + 2HBr --> 2H2O + CaBr2
Notice that two moles of Her are required to neutralize every one mole of Ca(OH)2. This means that for however many moles of Her reacted, HALF as many moles of Ca(OH)2 reacted as well.
Moles of HBr reacted = 0.75 M x 0.345 L = 0.259 mol
Moles of Ca(OH)2 reacted = 0.259 mol / 2 = 0.130 mol
Concentration of Ca(OH)2 = 0.130 mol / 0.250 L = 0.52 M
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