How many kilojoules of heat are absorbed when 40.7g of MgO(s) is decomposed into Mg(s) and O2 (g) at constant pressure?
-30.1 kj
Oh, it seems we have a chemistry question here! Let me do some quick math while trying to keep my jokes flowing.
To solve this, we need to use the concept of molar mass and stoichiometry. So, let's dive in!
The molar mass of MgO is 40.31 g/mol. Since we have 40.7 g of MgO, we can divide that by the molar mass to get the number of moles.
40.7 g / 40.31 g/mol ≈ 1.01 mol
According to the balanced chemical equation for the decomposition of magnesium oxide:
2 MgO(s) → 2 Mg(s) + O2(g)
We see that 2 moles of MgO result in 2 moles of Mg and 1 mole of O2. So, the number of moles of Mg and O2 will also be 1.01 mol.
Now, let's consider the enthalpy change of the reaction, which is the heat absorbed. It is given as -1203 kJ for the decomposition of 1 mole of MgO.
To find the heat absorbed for the given amount of MgO, we multiply the number of moles by the enthalpy change:
-1203 kJ/mol × 1.01 mol = -1214.03 kJ
Now, remember, my friend: negative values are always a little chilly, so the heat absorbed when 40.7 g of MgO is decomposed is approximately -1214.03 kJ.
Hope that helps, and I hope it brings a smile to your face!
To determine the amount of heat absorbed in the decomposition reaction, we need to use the concept of enthalpy of reaction. The enthalpy of reaction (∆H) is the heat change that occurs during a chemical reaction at constant pressure.
First, we need to find the balanced chemical equation for the decomposition of magnesium oxide (MgO):
2 MgO(s) -> 2 Mg(s) + O2(g)
Next, we need to find the molar mass of MgO. The molar mass of Mg is approximately 24.31 g/mol, and the molar mass of O is approximately 16.00 g/mol. So the molar mass of MgO is:
Mg: 24.31 g/mol
O: 16.00 g/mol
Total: 24.31 + 16.00 = 40.31 g/mol
Now, we can calculate the number of moles of MgO using the given mass:
Mass of MgO = 40.7g
Molar mass of MgO = 40.31 g/mol
Number of moles of MgO = (40.7g) / (40.31 g/mol)
Next, we need to use the stoichiometry of the balanced equation to determine the moles of Mg that is formed.
From the balanced equation, we can see that for every 2 moles of MgO, we get 2 moles of Mg. So:
Number of moles of Mg = (Number of moles of MgO) × (2 moles of Mg) / (2 moles of MgO)
Now, we can use the molar enthalpy of formation (∆Hf) values to calculate the heat absorbed in the decomposition reaction.
The standard enthalpy of formation for MgO is -601.8 kJ/mol, which means that for every mole of MgO formed, 601.8 kJ of heat is released. However, since we are decomposing MgO, we need to consider the reverse reaction. So, the enthalpy change for the decomposition of MgO is +601.8 kJ/mol.
Finally, we can calculate the heat absorbed in the decomposition reaction:
Heat absorbed = (Number of moles of Mg) × (∆H)
Let's calculate it:
2Mg + O2 ==> 2MgO
Look up dHf for MgO, which will be some number/mol and multiply by 2 for 2MgO.
See this link to find it.
http://en.wikipedia.org/wiki/Standard_enthalpy_change_of_formation_%28data_table%29
Then dHf x [(40.7/(2*40.3)] = ? and change the - sign to +.