When a 3.25 g sample of solid sodium hydroxide was dissolved in a calorimeter in 100 g of water, the temperature rose from 23.9 C to 32.0 C. Calculate delta H (in kJ/mol) of for the solution process:
NaOH (s) -> Na+(aq) + OH-(aq)
Use a calorimeter heat capacity of Ccal = 15.8 J/degrees C.
A 50 mL sample of a 1.00 M solution of CuSO4 is mised with 50 mL of 2.00 M KOH in a calorimeter. The temperature of both solutions was 20.2 C before mixing and 26.3C after mixing. The heat capacity of the calorimeter is 12.1 J/K. From this data, calculate the delta H for the process:
CuSO4(1 M) + 2KOH(2 M) - Cu(OH)2(s) + K2SO4(0.5 M)
q in joules = [mass H2O x specific heat H2O x (Tfinal-Tinitial)] + [Ccal x delta T].
delta H = q/3.25g for J/g
delta H = (q/3.25)*40 = J/mol
Convert to kJ/mol
Where did you get the 40 value?
tang ina nyO~
To calculate the delta H (enthalpy change) for each of these processes, we can use the equation:
delta H = q / n
where q is the heat absorbed or released in the process, and n is the number of moles involved in the process.
For the first question:
1. Calculate the heat absorbed (q) by the water using the equation:
q = m * C * delta T
where m is the mass of the water, C is the calorimeter heat capacity, and delta T is the change in temperature.
m = 100 g
C = 15.8 J/°C
delta T = 32.0°C - 23.9°C = 8.1°C
Substitute these values into the equation to find q.
q = 100 g * 15.8 J/°C * 8.1°C = 12,798 J
2. Calculate the number of moles (n) of NaOH using its molar mass.
molar mass of NaOH = 22.99 g/mol (Na) + 16.00 g/mol (O) + 1.01 g/mol (H)
= 39.00 g/mol
n = mass / molar mass
= 3.25 g / 39.00 g/mol
= 0.0833 mol
3. Now substitute the values of q and n into the equation to calculate delta H.
delta H = q / n
= 12,798 J / 0.0833 mol
= 153,560 J/mol
Since the answer is required in kJ/mol, divide the result by 1000.
delta H = 153,560 J/mol / 1000
= 153.56 kJ/mol
So, the delta H for the solution process of NaOH is 153.56 kJ/mol.
For the second question:
1. Calculate the heat absorbed (q) by the calorimeter using the equation:
q = C * delta T_calorimeter
where C is the heat capacity of the calorimeter and delta T_calorimeter is the change in temperature of the calorimeter.
C = 12.1 J/K
delta T_calorimeter = 26.3°C - 20.2°C = 6.1°C
Substitute these values into the equation to find q.
q = 12.1 J/K * 6.1°C = 73.81 J
2. Calculate the heat absorbed (q_solution) by the mixed solution using the equation:
q_solution = m_solution * C * delta T_solution
where m_solution is the sum of the volumes of the solutions, C is the heat capacity of the solution, and delta T_solution is the change in temperature of the solution.
m_solution = 50 mL + 50 mL = 100 mL = 0.1 L
C = 4.18 J/g°C (assuming the specific heat capacity of water)
delta T_solution = 26.3°C - 20.2°C = 6.1°C
Substitute these values into the equation to find q_solution.
q_solution = 0.1 L * 4.18 J/g°C * 6.1°C = 24.578 J
3. Calculate the total heat (q_total) absorbed or released in the process by summing q and q_solution.
q_total = q + q_solution = 73.81 J + 24.578 J = 98.388 J
4. Calculate the number of moles (n) involved in the reaction using the stoichiometric coefficients from the balanced chemical equation.
From the balanced chemical equation:
1 mol of CuSO4 reacts with 2 mol of KOH to produce 1 mol of Cu(OH)2 and 1 mol of K2SO4.
Therefore, since we have a 1:1 mole ratio of CuSO4 to Cu(OH)2, the number of moles (n) of CuSO4 is the same as the number of moles of Cu(OH)2.
n = M * V
= (1.00 mol/L) * (0.050 L)
= 0.050 mol
5. Now substitute the values of q_total and n into the equation to calculate delta H.
delta H = q_total / n
= 98.388 J / 0.050 mol
= 1,967.76 J/mol
Since the answer is required in kJ/mol, divide the result by 1000.
delta H = 1,967.76 J/mol / 1000
= 1.96776 kJ/mol
So, the delta H for the process of CuSO4 + 2KOH -> Cu(OH)2 + K2SO4 is 1.96776 kJ/mol.