The value of H° for the reaction below is -186 kJ. Calculate the heat (kJ) released when 25.0 g of HCl is produced.
H2(g) + Cl2(g) -> 2 HCl(g)
molar mass HCl is 36.5 so 2HCl = 73
So you get 186 kJ for 73 g HCl. You want to know kJ for 25.0 g. That's
186 kJ x (25.0/73) = ?
To calculate the heat (kJ) released when 25.0 g of HCl is produced, you can use the following steps:
Step 1: Calculate the moles of HCl produced.
To do this, we'll first determine the molar mass of HCl.
The molar mass of HCl = atomic mass of H + atomic mass of Cl
= (1.01 g/mol) + (35.45 g/mol)
= 36.46 g/mol
Next, we'll calculate the number of moles of HCl produced using the given mass and the molar mass of HCl.
Number of moles of HCl = mass of HCl / molar mass of HCl
= 25.0 g / 36.46 g/mol
≈ 0.686 mol
Step 2: Calculate the heat released using the given reaction's enthalpy change (ΔH°) and the stoichiometric coefficients.
From the balanced equation:
1 mole of H2 produces 2 moles of HCl.
Therefore, according to the stoichiometric coefficients, we can say that
0.686 mol of H2 produces 0.686 * 2 mol of HCl.
The heat released can be calculated using the following formula:
Heat released = ΔH° × moles of HCl produced
= -186 kJ/mol × (0.686 * 2 mol)
= -186 kJ/mol × 1.372 mol
≈ -255.672 kJ
Therefore, the heat released when 25.0 g of HCl is produced is approximately -255.672 kJ.
To calculate the heat released when 25.0 g of HCl is produced, we can use the concept of stoichiometry and the given value of ΔH° for the reaction.
Step 1: Convert grams of HCl to moles.
To do this, we need to determine the molar mass of HCl, which is calculated as follows:
Molar mass of H = 1.01 g/mol
Molar mass of Cl = 35.45 g/mol
Molar mass of HCl = 1.01 g/mol + 35.45 g/mol = 36.46 g/mol
Using the molar mass, we can calculate the number of moles of HCl:
25.0 g HCl * (1 mol / 36.46 g) = 0.686 mol HCl
Step 2: Use the stoichiometry of the balanced equation to relate the moles of HCl to the moles of reactants.
From the balanced equation, we can see that 2 moles of HCl are produced for every 1 mole of H2. Therefore, the number of moles of H2 can be calculated as follows:
0.686 mol HCl * (1 mol H2 / 2 mol HCl) = 0.343 mol H2
Similarly, we can calculate the number of moles of Cl2 as follows:
0.686 mol HCl * (1 mol Cl2 / 2 mol HCl) = 0.343 mol Cl2
Step 3: Calculate the heat released using the given ΔH° value.
Since the given value of ΔH° is in kJ, we can directly use it in the calculation. According to the balanced equation, the reaction releases 186 kJ of heat when 2 moles of HCl are produced.
To determine the heat released when 0.686 mol of HCl is produced, we can set up the following proportion:
0.686 mol HCl / 2 mol HCl = x kJ / 186 kJ
Solving for x, we get:
x = (0.686 mol HCl / 2 mol HCl) * 186 kJ = 64.767 kJ
Therefore, the heat released when 25.0 g of HCl is produced is approximately 64.767 kJ.