How much heat (in kilojoules) is liberated by the combustion of 7.01 g of magnesium? Include the sign in your answer. H+-1203kJ
2Mg + O2 ==> 2MgO + 1203 kJ (although I can't tell if you meant that to be a + or a -).
You know from the equation that 2 mol Mg (which is 2*24.3 g Mg) liberates 1203 kJ/
So 1203 kJ x 7.01/(2*24.3) = ? and you place the right sign on it.
To calculate the amount of heat liberated by the combustion of magnesium, we need to use the enthalpy of combustion, also known as the heat of combustion. The enthalpy of combustion is the amount of heat released when one mole of a substance undergoes complete combustion.
1. Start by writing the balanced chemical equation for the combustion of magnesium:
2 Mg + O2 → 2 MgO
2. Determine the molar mass of magnesium (Mg):
The molar mass of Mg is 24.305 g/mol.
3. Convert the given mass of magnesium (7.01 g) to moles:
moles of Mg = mass of Mg / molar mass of Mg
moles of Mg = 7.01 g / 24.305 g/mol
4. Since the stoichiometry of the balanced equation implies that 2 moles of Mg are required to produce 2 moles of MgO, we have a 1:1 mole ratio. Hence, the moles of MgO formed is also 7.01 g / 24.305 g/mol.
5. Now, we need to use the enthalpy change given for the reaction, which is -1203 kJ (negative sign indicates heat release).
6. Calculate the heat liberated by the combustion:
Heat liberated = moles of MgO formed × enthalpy of combustion
Heat liberated = (7.01 g / 24.305 g/mol) × -1203 kJ
To get the final answer, perform the calculations:
7. Calculate the moles of MgO formed:
moles of MgO = 7.01 g / 24.305 g/mol = 0.288 mol
8. Calculate the heat liberated:
Heat liberated = 0.288 mol × -1203 kJ/mol
Therefore, the amount of heat liberated by the combustion of 7.01 g of magnesium is -346.464 kJ (rounded to three decimal places). The negative sign indicates that heat is being released during the combustion.