A 2.50-g sample of powdered zinc is added to 100.0 mL of a 2.00-M aqueous solution of hydrobromic acid in a calorimeter. The total heat capacity of the calorimeter and solution is 448 J/K. The observed increase in temperature is 21.1 K at a constant pressure of one bar. Using these data, calculate the standard enthalpy of reaction.

mols Zn = grams/molar mass = approximately 0.04 mol (but this is an estimate) and Zn is the limiting reagent.

Zn + 2HBr ==> H2 + ZnBr2
qrxn = Ccal x delta T.

qrxn/mol = [qrxn/mols Zn] = ?

To calculate the standard enthalpy of reaction, we can use the equation:

ΔH = q / n

where ΔH is the standard enthalpy of reaction, q is the heat absorbed or released during the reaction, and n is the number of moles of the limiting reactant.

First, we need to determine the heat absorbed or released during the reaction. We can use the equation:

q = (m × C × ΔT) + (Csol × ΔT)

where q is the heat absorbed or released, m is the mass of the limiting reactant (zinc in this case), C is the heat capacity of the calorimeter and solution, ΔT is the change in temperature, and Csol is the heat capacity of the solution (which we can assume is the same as the heat capacity of water).

Let's calculate each term step by step:

1. Calculate the moles of zinc:
To find the number of moles of zinc, we can use its molar mass (which is 65.38 g/mol):

moles of zinc = mass of zinc / molar mass of zinc
= 2.50 g / 65.38 g/mol

2. Calculate the heat absorbed or released by the reaction (q):

q = (2.50 g × C × ΔT) + (Csol × ΔT)

We are given that the total heat capacity (C) of the calorimeter and solution is 448 J/K, and the change in temperature (ΔT) is 21.1 K. We need to convert the mass of zinc to moles:

q = (moles of zinc × C × ΔT) + (Csol × ΔT)

3. Calculate the standard enthalpy of reaction (ΔH):

ΔH = q / n

where n is the moles of zinc.

Now we can substitute the values into the equation to calculate the standard enthalpy of reaction.