Consider the following reaction.
2Fe2O3 --> 4Fe+3O2 Hrxn=+824.2
The Formation of 21.0 of Fe results in
1)the release of 77.5 kJ of heat.
2)the absorption of 3.10 × 102 kJ of heat.
3)the release of 4330 kJ of heat.
4)the absorption of 77.5 kJ of heat.
5)the release of 3.10 × 102 kJ of heat.
6)the absorption of 4330 kJ of heat.
Decomposition of ionic solids are usually endothermic. So throw out 1, 3, & 5.
Convert 21g Fe to moles and use the equation ratios.
To determine the heat released or absorbed in the formation of 21.0 g of Fe, we need to use the given enthalpy change of the reaction, which is +824.2 kJ (positive because it is an endothermic reaction).
The enthalpy change is given in kJ, and we want to find the heat released or absorbed when 21.0 g of Fe is formed. So, we need to calculate the moles of Fe involved in the reaction.
1 mol of Fe2O3 produces 4 mol of Fe.
Molar mass of Fe2O3 = (2)(55.85 g/mol) + (3)(16.00 g/mol) = 159.70 g/mol
Molar mass of Fe = 55.85 g/mol
(21.0 g Fe2O3) x (1 mol Fe2O3 / 159.70 g Fe2O3) x (4 mol Fe / 1 mol Fe2O3) = 0.524 mol Fe
Now, we can calculate the heat released or absorbed using the given enthalpy change:
Heat released or absorbed (in kJ) = moles of Fe x enthalpy change (in kJ/mol)
Heat released or absorbed = (0.524 mol Fe) x (+824.2 kJ/mol)
Heat released or absorbed = -431.57 kJ
The negative sign indicates that heat is released during the formation of 21.0 g of Fe.
So, the correct answer is:
5) the release of 3.10 × 102 kJ of heat.
To solve this problem, we need to use the given heat of reaction (Hrxn) and the stoichiometry of the reaction.
The given reaction is:
2Fe2O3 → 4Fe + 3O2
We are given that the heat of reaction (Hrxn) is +824.2 kJ.
From the stoichiometry of the reaction, we can see that the balanced equation tells us that 2 moles of Fe2O3 form 4 moles of Fe. Therefore, the stoichiometric factor between Fe and Fe2O3 is 4/2 = 2.
Now, we can calculate the heat released or absorbed for the formation of a certain amount of Fe.
Let's say x moles of Fe are formed. Since the stoichiometric factor between Fe and Fe2O3 is 2, the amount of Fe2O3 consumed will be 2x moles.
Using the given heat of reaction (Hrxn), we can set up the following proportion:
(Hrxn / 2 moles of Fe2O3) = (x moles of Fe / heat released or absorbed)
Now, we can substitute the given values into the equation and solve for the heat released or absorbed.
Given:
Hrxn = +824.2 kJ
Using the proportion:
824.2 kJ / 2 mol = x mol / heat released or absorbed
Now, we can calculate the heat released or absorbed when 21.0 moles of Fe are formed.
824.2 kJ / 2 mol = 21.0 mol / heat released or absorbed
Cross-multiplying gives us:
(824.2 kJ) x (heat released or absorbed) = (2 mol) x (21.0 mol)
Simplifying:
(824.2 kJ) x (heat released or absorbed) = 42 mol^2
Dividing both sides by 824.2 kJ gives us:
heat released or absorbed = (42 mol^2) / (824.2 kJ)
Calculating this expression gives us the answer.
Therefore, to determine the correct option, we need to solve the equation (42 mol^2) / (824.2 kJ) and choose the option that matches the calculated value.