Consider the reaction
2 Al2O3(s) -> 4 Al(s) + 3 O2(g) .
�H = +3339.6 kJ/mol
What is the change in heat when 0.455 L of a 3.60 M Al solution reacts with excess O2 ?
1. -685 kJ
2. -21,962 kJ
3. -1368 kJ
4. -2738 kJ
5. -5477 kJ
6. -26,521 kJ
7. -424 kJ
8. -1695 kJ
To find the change in heat when 0.455 L of a 3.60 M Al solution reacts with excess O2, we can use the concept of stoichiometry and the enthalpy change of the reaction.
First, let's calculate the moles of Al in the solution:
0.455 L * 3.60 mol/L = 1.638 mol Al
Since the reaction is 2 Al2O3(s) -> 4 Al(s) + 3 O2(g), we can see that for every 2 moles of Al2O3, we get 4 moles of Al.
Therefore, the moles of Al2O3 that will react can be calculated as follows:
1.638 mol Al * 1 mol Al2O3 / 4 mol Al = 0.410 mol Al2O3
Now we can calculate the change in heat using the given enthalpy change of the reaction:
Change in heat = moles of Al2O3 * ΔH
Change in heat = 0.410 mol Al2O3 * 3339.6 kJ/mol Al2O3
Change in heat = -1366.0 kJ
So, the change in heat when 0.455 L of a 3.60 M Al solution reacts with excess O2 is approximately -1368 kJ.
Therefore, the correct answer is option 3: -1368 kJ.
To find the change in heat when the reaction occurs, we need to calculate the amount of heat released or absorbed using the given values and the stoichiometry of the reaction. Here are the steps to find the answer:
1. Calculate the moles of Al reacted:
The volume of the Al solution is given as 0.455 L, and the concentration is 3.60 M. Therefore, the moles of Al in the solution can be calculated as follows:
Moles of Al = Volume × Concentration
= 0.455 L × 3.60 mol/L
2. Use the stoichiometry of the reaction to find the moles of Al2O3 reacted:
From the balanced equation, the stoichiometric ratio between Al and Al2O3 is 4:2. Therefore, moles of Al2O3 reacted can be calculated as follows:
Moles of Al2O3 = (Moles of Al / 4) × 2
3. Calculate the heat released or absorbed using the equation ΔH = -n × ΔHf:
ΔH represents the change in heat, n represents the stoichiometric coefficient of the substance involved in the reaction, and ΔHf represents the standard enthalpy of formation. In this case, we use the value for ΔH as given in the question.
4. Substitute the values into the equation:
ΔH = (Moles of Al2O3) × ΔH
5. Convert the result to kilojoules (kJ):
Divide the answer by 1000 to convert the value from joules to kilojoules.
6. Round the answer to the correct number of significant figures.
Now, let us follow these steps to find the correct option from the given choices.
-2738
Molarity = moles/Liters so moles = Molarity * Liters
moles = 3.60 M * .455 L = 1.64 moles of Al
1.64 moles Al / 4 moles Al = .4095 (this number is how many times the reaction can be done) .4095 moles * -3339.6 kj/mol (negative because you're doing reverse reaction and reverse reaction is reversed heat) = -1368 kj
answer = -1368 kj