Calculation of )Hf0 for Mg2+(aq.)
1. Assume the heat capacity of the final solution is 3.92 J K-1 g-1. Using the mass of the HCl
solution, calculate qcontents from equation (4.6). Calculate qsystem from equation (4.5).
2. Calculate the moles of Mg2+ produced, nrxn. Be sure to identify the limiting reagent in the
reaction.
3. Calculate the molar enthalpy change, )H0 rxn, for reaction (4.19). This is the same as )H0f for
Mg2+(aq.).Calculation of )Hf0 for MgO(s)
Calculation of delta Hf for MgO(s)
1. Again, assume the heat capacity of the final solution is 3.92 J K-1 g-1. Calculate qcontents and
qsystem.
2. Calculate the number of moles of Mg2+ (aq.) produced, nrxn.
3. Calculate the standard molar enthalpy change for reaction (4.20).
4. Average the values for )H0 rxn for part I and average the values for )H0
rxn for part II. Using these average values, calculate )H0f of MgO(s).
Questions
1. Why are both the mass and the volume of the hydrochloric acid solution recorded?
2. In this experiment it was assumed that the calorimeter neither absorbed nor released heat
(i.e., qcalorimeter = 0), but this is almost certainly not the case. Would the measured value of
)H0f (Mg2+(aq.)) be more or less exothermic if the calorimeter absorbed heat (that is, if
qcalorimeter > 0)? Explain why.
3. Explain why )H0rxn, for reaction (4.19) is the same as )H0f for Mg2+(aq.).
4. Use tabulated standard molar enthalpies of formation (from the textbook) to calculate )H0
rxn
for the following reactions:
1. 2NO(g) + O2(g) v 2NO2(g)
2. 2H2S(g) + 3O2(g) v 2SO2(g) + 2H2O(g)
3. Fe2O3(s) + 3CO(g) v Fe(s) + 3CO2(g)
5. Calcium sulphate reacts with carbon (in the form of graphite) according to the reaction:
CaSO4(s) + 1/2C(s, graphite) v CaO(s) + SO2(g) + 1/2CO2(g)
When 204.2 g of CaSO4(s) reacts with excess graphite at 298.15 K and 1 atm pressure, 456
kJ of heat are absorbed. Calculate the standard molar enthalpy of formation of CaSO4(s).
.
Data
Magnesium and hydrochloric
Run#1
mass of calorimeter+HCl/g =193.89g
mass of calorimeter/g=134.24g
mass og HCl/g=59.65g
mass of 50 mL beaker+Mg/g=30.7885g
mass of 50mL beaker/g=30.5655g
mass of Mg/g 0.2230g
initial temp22degree
after3min,after addingMg=20.1
final temp 30.1
run#2
mass of calorimeter+HCl/g =191.85g
mass of calorimeter/g=132.04g
mass og HCl/g=59.81g
mass of 50 mL beaker+Mg/g=31.7475g
mass of 50mL beaker/g=31.574g
mass of Mg/g 0.1727g
initial temp23degree
after3min,after addingMg=20.1
final temp 30.1
Part 2 Magnesium oxide+Hydrochloric
Run#1 Acid
mass of calorimeter+HCl/g =192.49g
mass of calorimeter/g=131.26g
mass og HCl/g=61.23g
mass of 50 mL beaker+Mg/g=32.2601g
mass of 50mL beaker/g=31.5502g
mass of Mg/g 1.2601g
initial temp23.5degree
after3min,after addingMgO=20.0
final temp 28.0
run#2
mass of calorimeter+HCl/g =190.56g
mass of calorimeter/g=131.52g
mass og HCl/g=59.04g
mass of 50 mL beaker+Mg/g=32.2486g
mass of 50mL beaker/g=31.5532g
mass of Mg/g 0.6954g
initial temp24degree
after3min,after addingMgO=20.0
final temp 28.0
I am greatly appreciate your help.. Sad
A pan containing 250 grams of water at 100oC is boiled dry. How many calories of heat are required to convert the liquid H2O to gaseous H2O?
I'm sorry to hear that you're feeling sad. I'll do my best to help you with your questions. Let's start with question 1.
1. The mass and the volume of the hydrochloric acid solution are recorded because they are needed for the calculations in the experiment. The mass is used to calculate the amount of heat transferred to the solution and the volume is used to determine the concentration of the solution.
Now let's move on to question 2.
2. If the calorimeter absorbed heat (qcalorimeter > 0), the measured value of ΔH0f (Mg2+(aq.)) would be less exothermic. This is because the heat absorbed by the calorimeter would reduce the amount of heat transferred to the system (the reaction). Consequently, the measured enthalpy change would be lower than the actual value.
Next, let's address question 3.
3. ΔH0rxn for reaction (4.19) is the same as ΔH0f for Mg2+(aq.) because both values represent the enthalpy change for the formation of one mole of Mg2+(aq.) from its constituent elements in their standard states. In other words, the enthalpy change for the reaction is equal to the enthalpy change for the formation of the product.
Moving on to question 4.
4. To calculate ΔH0rxn for the given reactions, you need to use the tabulated standard molar enthalpies of formation (ΔH0f) for each compound involved. The equation to calculate ΔH0rxn is as follows:
ΔH0rxn = ∑ (n ΔH0f of products) - ∑ (n ΔH0f of reactants)
where n is the stoichiometric coefficient of each compound. You can find the ΔH0f values in a textbook or a reliable reference source.
Finally, let's address question 5.
5. To calculate the standard molar enthalpy of formation of CaSO4(s), you need to use the given heat absorbed (456 kJ), the number of moles of CaSO4 reacted (calculated from the given mass), and the stoichiometric coefficients of CaSO4 and the other compounds in the balanced equation. The equation to calculate ΔH0f is similar to the one for question 4:
ΔH0f = ΔH0rxn / (moles of CaSO4)
I hope this helps. If you have any further questions, please let me know.
I'll do my best to help you understand the calculations and answer your questions. Let's break it down step by step:
1. Calculation of ΔHf0 for Mg2+(aq.):
- In this calculation, you need to determine the enthalpy change of the system and the contents (solution).
- To calculate qcontents, you need to use equation (4.6), which states qcontents = mass solution x heat capacity x ΔT, where ΔT is the change in temperature.
- To calculate qsystem, you need to use equation (4.5), which states qsystem = -qcontents. This is because the heat lost by the system is gained by the surroundings.
2. Calculate the moles of Mg2+ produced, nrxn:
- To calculate the moles of Mg2+ produced, you need to know the amount of Mg used and the balanced chemical equation for the reaction.
- Identify the limiting reagent in the reaction, which is the reactant that is completely consumed and determines the amount of product formed.
3. Calculate the molar enthalpy change, ΔH0rxn, for reaction (4.19):
- The molar enthalpy change for reaction (4.19) is the same as the standard molar enthalpy of formation, ΔH0f, for Mg2+(aq.).
- You need to use the balanced chemical equation and the molar enthalpies of formation of the reactants and products to calculate ΔH0rxn.
4. Calculation of ΔHf0 for MgO(s):
- The process for calculating ΔHf0 for MgO(s) is similar to the previous calculation.
- Again, you need to determine the enthalpy change of the system and the contents (solution) using the given data.
- Calculate the moles of Mg2+ (aq.) produced.
- Calculate the standard molar enthalpy change for reaction (4.20).
- Average the values of ΔH0rxn for part I and II to calculate ΔH0f of MgO(s).
Now, let's move on to the specific questions:
1. Both the mass and volume of the hydrochloric acid solution are recorded because they are needed to calculate the amount of substance (moles). Mass is used to calculate the moles of the solute, while volume is used to calculate the concentration (moles per liter) of the solution.
2. If the calorimeter absorbs heat (qcalorimeter > 0), it would make the measured value of ΔH0f (Mg2+(aq.)) less exothermic. This is because the heat absorbed by the calorimeter is not accounted for in the calculation of the system's enthalpy change, resulting in a lower value.
3. ΔH0rxn for reaction (4.19) is the same as ΔH0f for Mg2+(aq.) because the reaction represents the formation of Mg2+(aq.) from its constituent elements in their standard states. The standard molar enthalpy of formation directly corresponds to the enthalpy change for this reaction.
4. To calculate ΔH0rxn for the given reactions, you need to use the tabulated standard molar enthalpies of formation for the reactants and products. Subtract the sum of the molar enthalpies of formation of the reactants from the sum of the molar enthalpies of formation of the products to obtain ΔH0rxn.
5. To calculate the standard molar enthalpy of formation of CaSO4(s), you need to use the given data and equations. Calculate the amount of heat absorbed (q) using the mass, specific heat capacity, and temperature change. From the balanced chemical equation, determine the moles of CaSO4. Divide the heat absorbed by the moles of CaSO4 to get the standard molar enthalpy of formation.
I hope this explanation helps you understand the calculations and answers to your questions. Let me know if there's anything else I can assist you with!