Given the thermochemical equation below, calculate the amount of energy released when 250. g of NaOH (molar mass = 40.0 g/mol) reacts with an excess of HCl. Report answer to the correct number of significant figures in units of kilojoules, kJ.
NaOH + HCl --> NaCl + H2O deltaH = -56.2 kJ/mol
kJ released = 56.2 kJ/mol x (250/40) = ?
To calculate the amount of energy released when 250. g of NaOH reacts with an excess of HCl, we need to follow these steps:
1. Convert the given mass of NaOH into moles.
- Number of moles = Given mass / Molar mass
Given mass of NaOH = 250. g
Molar mass of NaOH = 40.0 g/mol
Number of moles of NaOH = 250. g / 40.0 g/mol
= 6.25 mol
2. Use the thermochemical equation and the deltaH value to calculate the energy released.
- The deltaH value given in the equation is -56.2 kJ/mol.
Energy released = Number of moles of NaOH * deltaH
Energy released = 6.25 mol * -56.2 kJ/mol
= -350.625 kJ
3. Round the answer to the correct number of significant figures.
- The given mass (250. g) has 3 significant figures, so the answer should also have 3 significant figures.
Rounded energy released = -350. kJ
Therefore, the amount of energy released when 250. g of NaOH reacts with an excess of HCl is -350. kJ. Note that the negative sign indicates energy release.