Elements A and B react together according to the following reaction:

Question

2 A + B2 → 2 AB
The molar mass of A is 23.0 g/mol. The molar mass of B is 35.5 g/mol. If the goal is to
produce 140 g of AB, how many grams of A would be needed initially?
(1 point)
70.0 g of A
42.0 grams of A
55.0 grams of A
35.5 grams of A

Answer 1

To find out how many grams of A are needed to produce 140 g of AB, we will first determine the molar mass of AB and then use stoichiometry based on the balanced chemical equation.

1. Calculate the molar mass of AB:

   \[ \text{Molar mass of AB} = \text{Molar mass of A} + \text{Molar mass of B} = 23.0 , \text{g/mol} + 35.5 , \text{g/mol} = 58.5 , \text{g/mol} \]

2. Determine moles of AB produced:

   To find the number of moles of AB made from 140 g:

   \[ \text{Moles of AB} = \frac{\text{mass of AB}}{\text{molar mass of AB}} = \frac{140 , \text{g}}{58.5 , \text{g/mol}} \approx 2.396 , \text{mol} \]

3. Use the stoichiometry of the reaction:

   From the balanced equation: \[ 2 A + B_2 \rightarrow 2 AB \] We see that 2 moles of A produce 2 moles of AB. Thus, the moles of A required are equal to the moles of AB produced (1:1 ratio):

   \[ \text{Moles of A} = 2.396 , \text{mol} \]

4. Calculate the mass of A needed:

   Now, we find the grams of A needed:

   \[ \text{Mass of A} = \text{Moles of A} \times \text{Molar mass of A} \] \[ \text{Mass of A} = 2.396 , \text{mol} \times 23.0 , \text{g/mol} \approx 55.1 , \text{g} \]

Thus, the closest answer option is:

55.0 grams of A.