Given:
H3PO4(aq) + 3 NaOH(aq) �¨ 3 H2O(l) + Na3PO4(aq)
ĢH = -166.5 kJ
What is the value for q (heat) if 4.00 g of NaOH reacts with an excess of H3PO4?
Please can you explain to me HOW to do this, not just give me an answer?
Thanks!
The heat of reaction has the wrong units...it should be -166.5kJ/MoleNa3PO4
So, the question is, the reaction calls for three moles (120g) of NaOH, so you will get 4/120 fraction of the heat of reaction.
Given:
H3PO4(aq) + 3 NaOH(aq) yields 3 H2O(l) + Na3PO4(aq)
change in H = -166.5 kJ
What is the value for q (heat) if 4.00 g of NaOH reacts with an excess of H3PO4?
Please can you explain to me HOW to do this, not just give me an answer?
Thanks!
To find the value for q (heat), you need to calculate the amount of heat absorbed or released during the reaction. This can be done using the equation:
q = m * ƒ´H
Where:
q = heat (in joules)
m = mass of the substance (in grams)
ƒ´H = enthalpy change (in joules per mole)
First, you need to convert the mass of NaOH (4.00 g) to moles. To do this, you need to know the molar mass of NaOH.
The molar mass of NaOH is calculated by adding the atomic masses of its constituent elements:
Na: 22.99 g/mol
O: 16.00 g/mol
H: 1.01 g/mol
Molar mass of NaOH = 22.99 g/mol + 16.00 g/mol + 1.01 g/mol = 40.00 g/mol
Next, calculate the number of moles of NaOH:
moles = mass / molar mass
moles of NaOH = 4.00 g / 40.00 g/mol = 0.100 mol
Since the balanced chemical equation tells us that 1 mole of NaOH reacts with 1 mole of H3PO4, we can infer that 0.100 mol of NaOH reacts with 0.100 mol of H3PO4.
Now, we can use the equation ƒ´H = -166.5 kJ to calculate the value of q.
However, the enthalpy change is given in kJ, so we need to convert it to joules by multiplying by 1000:
ƒ´H = -166.5 kJ * 1000 J/kJ = -166,500 J/mol
Since the balanced chemical equation tells us that 3 moles of H2O are produced per mole of NaOH, we can conclude that 0.100 mol of NaOH will produce 0.100 mol * 3 = 0.300 mol of H2O.
Now, we can calculate the value of q using the equation:
q = moles * ƒ´H
q = 0.300 mol * -166,500 J/mol = -49,950 J
Therefore, the value for q (heat) is -49,950 J.