1) A quantity of 85 mL of .900 M HCl is mixed with 85 mL of .900 M KOH in a constant-pressure calorimeter that has a heat capacity of 325 J/C. If the initial temperatures of both solutions are the same at 18.24 degrees C, what is the final temperature of the mixed solution?
2) A 2.10-mole sample of crystalline acetic acid, initially at 17 degrees C, is allowed to melt at 17 degrees C and is then heated to 118.1 degrees C (its normal boiling point) at 1 atm. The sample is allowed to vaporize at 118.1 degrees C and is then rapidly quenched to 17 degrees C, so that it re-crystalizes. Calculate delta(H) for the total process described
3) The combustion of what volume of ethane (C2H6), measured at 23 degrees C and 752 mmHg, would be required to heat 855 g of water from 25 degrees C to 98 degrees C?
3.
How much heat (q) is needed to heat the water.
q = mass H2O x specific heat H2O x (Tfinal-Tinitial) = approx 250,000 but that is an estimate as are all of the other numbers that follow.
Look up the heat combustion for ethane, probably given in kJ/mol
Convert that to the number of mols needed to provide the q from the first part, then convert mols to volume in L at the condition listed.
Post your work if you get stuck.
2. I've been thinking about this and I can't see a good reason why it isn't zero. It absorbs heat on the way up to vapor and releases heat on the way back down to the crystalline state. Think about that, is that right? If that is true it sure would save a lot of calculating time.
To solve these questions, we need to use various thermodynamic equations and principles. I'll break down each question and explain the steps to get the answers.
1) To find the final temperature of the mixed solution, we can use the principle of energy conservation, which states that the total energy of a closed system remains constant. The equation we'll use is:
q(initial solution) + q(final solution) + q(calorimeter) = 0
Here's how we can determine the final temperature:
i) Calculate the heat gained or lost by the initial solution (HCl):
q(initial solution) = (mass of initial solution) * (specific heat of water) * (change in temperature)
= (85g H2O + 85g HCl) * (4.184 J/g·°C) * (final temperature - 18.24°C)
ii) Calculate the heat gained or lost by the final solution (mixed HCl and KOH):
q(final solution) = (mass of final solution) * (specific heat of water) * (change in temperature)
= (170g mixture) * (4.184 J/g·°C) * (final temperature - initial temperature)
iii) Calculate the heat gained or lost by the calorimeter:
q(calorimeter) = (calorimeter heat capacity) * (change in temperature)
= (325 J/°C) * (final temperature - 18.24°C)
iv) Substitute the calculated values into the energy conservation equation and solve for the final temperature.
2) To determine delta(H) for the process described, we need to calculate the enthalpy change for each step and then sum them up.
i) Melting the acetic acid at its melting point: The enthalpy change for this step is called the heat of fusion (delta(H)fus). You can usually find this value in a reference table. Multiplying this value by the number of moles will give you the enthalpy change for the melting process.
ii) Heating the melted acetic acid to its boiling point: The enthalpy change for this step is called the heat capacity (Cp). You can also find this value in a reference table. Multiply Cp by the number of moles and the change in temperature.
iii) Vaporizing the acetic acid at its boiling point: The enthalpy change here is called the heat of vaporization (delta(H)vap). Find this value in a reference table and multiply it by the number of moles.
iv) Cooling the vaporized acetic acid back to the initial temperature: Use the heat capacity (Cp) again to determine the enthalpy change during this cooling process.
Finally, sum up the enthalpy changes from each step to find the total delta(H) for the process.
3) To find the volume of ethane needed for the combustion process, we'll use the ideal gas law and the concept of stoichiometry.
i) Calculate the number of moles of water:
n(H2O) = (mass of water) / (molar mass of water)
ii) Use the given temperature and pressure to determine the volume of water using the ideal gas law:
V(H2O) = (n(H2O) * R * T) / P
(where R is the ideal gas constant, T is the temperature in Kelvin, and P is the pressure in atm)
iii) Convert the volume of water to liters and calculate the volume of ethane using the balanced chemical equation and stoichiometry:
C2H6 + 7/2 O2 -> 2CO2 + 3H2O
The stoichiometric ratio between ethane and water is 1 to 3, so the volume of ethane is:
V(C2H6) = V(H2O) / 3
That's how you can calculate the volume of ethane required for the combustion of water.
Remember to ensure your units are consistent and that you use the correct values from reference tables or other reliable sources.
1.
mass H2O = 85 g + 85 g = ?
(mass H2O x specific heat H2O x (Tfinal-Tinitial) + Ccal*(Tfinal-Tinitial) = 0
Substitute and solve for Tf.