The melting of 0.140 g of Br2 (which occurs at -7.2 C at 1 atm pressure) absorbs 9.43 J of heat. Compute the enthalpy change in 2.00 mol of Br2 when it freezes.
Convert 2.00 mol Br2 to grams.
moles = grams/molar mass.
9.43 J x (? g Br2/0.140 g Br2) = xx J.
To compute the enthalpy change when 2.00 mol of Br2 freezes, we need to first calculate the enthalpy change per mole of Br2 during the freezing process.
We know that the melting of 0.140 g of Br2 absorbs 9.43 J of heat. So, we can calculate the enthalpy change per gram of Br2 using the following equation:
Enthalpy change per gram (ΔH) = heat absorbed (q) / mass of Br2 (m)
The mass of Br2 can be calculated using its molar mass, which is equal to 159.808 g/mol.
mass of Br2 (m) = molar mass of Br2 (M) * Number of moles (n)
Once we have calculated the enthalpy change per gram, we can convert it to the enthalpy change per mole using the molar mass:
Enthalpy change per mole of Br2 = Enthalpy change per gram of Br2 * (1 / molar mass of Br2)
Finally, we can use this value to calculate the enthalpy change in 2.00 mol of Br2:
Enthalpy change = Enthalpy change per mole of Br2 * Number of moles
Now, let's calculate it step by step:
Step 1: Calculate the mass of Br2 in grams
mass of Br2 (m) = molar mass of Br2 (M) * Number of moles (n)
mass of Br2 (m) = 159.808 g/mol * 0.140 g = 22.372 g
Step 2: Calculate the enthalpy change per gram
Enthalpy change per gram (ΔH) = heat absorbed (q) / mass of Br2 (m)
Enthalpy change per gram (ΔH) = 9.43 J / 22.372 g = 0.421 J/g
Step 3: Convert the enthalpy change per gram to per mole
Enthalpy change per mole of Br2 = Enthalpy change per gram of Br2 * (1 / molar mass of Br2)
Enthalpy change per mole of Br2 = 0.421 J/g * (1 / 159.808 g/mol) = 0.002634 J/mol
Step 4: Calculate the enthalpy change in 2.00 mol of Br2
Enthalpy change = Enthalpy change per mole of Br2 * Number of moles
Enthalpy change = 0.002634 J/mol * 2.00 mol = 0.005268 J/mol
Therefore, the enthalpy change in 2.00 mol of Br2 when it freezes is 0.005268 J/mol.