high purtity benzoic acid (C6H5COOH; ^Hrxn for combustion is -3227kJ/mol) is used as a standard for calibrating bomb calorimeters. A 1.221g sample burns in a calorimeter(heat capacity=1365J/C) that contains exactly 1.270kg of H2O. What temperature change was observed?
Calculate mols benzoic acid used.
Convert delta H/mol to delta H/mols benzoic acid used. I'll call that q.
1365 J/C x Y degrees = q.
Solve for Y. Don't forget to keep the units straight. The calorimeter constant is given in J/C while the benzoic acid delta H is in kJ/mol.
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To determine the temperature change observed during the combustion of benzoic acid, we can use the equation:
q = mcΔT
Where:
q is the heat absorbed or released during the reaction
m is the mass of the substance
c is the specific heat capacity of the substance
ΔT is the change in temperature
First, let's calculate the heat released during the combustion of benzoic acid.
1. Calculate the moles of benzoic acid burned:
Molar mass of benzoic acid (C6H5COOH) = 122.12 g/mol
moles = mass / molar mass
moles = 1.221 g / 122.12 g/mol
moles = 0.01 mol (rounded to two decimal places)
2. Calculate the heat released during the combustion:
ΔHrxn = -3227 kJ/mol
q = moles * ΔHrxn
q = 0.01 mol * -3227 kJ/mol
q = -32.27 kJ
Since energy is released during combustion, the q value is negative (-32.27 kJ).
Now we can calculate the temperature change observed using the heat capacity of water.
3. Convert the heat release to joules:
1 kJ = 1000 J
q = -32.27 kJ * 1000 J/kJ
q = -32270 J
4. Calculate the temperature change:
q = mcΔT
Rearranging the formula, we get:
ΔT = q / (mc)
m = mass of water = 1.27 kg
c = specific heat capacity of water = 4.18 J/g°C (or 4180 J/kg°C)
ΔT = -32270 J / (1.27 kg * 4180 J/kg°C)
ΔT = -6.11 °C
Since the q value is negative, indicating that heat is released during the reaction, the temperature change observed is a decrease of 6.11 °C.