How many grams of each species will be present at the end when 0.500 g of copper is added to 2.500 g of AgNO3?

Answer : The mass of excess ,  and Ag is, 1.16 g, 0.992 g and 0.849 g respectively.

Solution : Given,

Mass of Cu = 0.500 g

Mass of = 2.500 g

Molar mass of Cu = 63.5 g/mole

Molar mass of Ag = 108 g/mole

Molar mass of = 170 g/mole

Molar mass of = 126 g/mole

First we have to calculate the moles of Cu and .

Now we have to calculate the limiting and excess reagent.

The balanced chemical reaction is,

From the balanced reaction we conclude that

As, 1 mole of react with 1 mole of

So, 0.00787 moles of react with 0.00787 moles of

From this we conclude that, is an excess reagent because the given moles are greater than the required moles and is a limiting reagent and it limits the formation of product.

Now we have to calculate the moles of excess

Moles of excess  = 0.0147 - 0.00787 = 0.00683 moles

Now we have to calculate the moles of  and Ag.

From the reaction, we conclude that

As, 1 mole of react to give 1 mole of

So, 0.00787 moles of react to give 0.00787 moles of

and,

As, 1 mole of react to give 1 mole of

So, 0.00787 moles of react to give 0.00787 moles of

Now we have to calculate the mass of excess ,  and Ag.

and,

and,

Thus, the mass of excess ,  and Ag is, 1.16 g, 0.992 g and 0.849 g respectively.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

a is the correct answer