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Preparatory Questions (2 pt) The heat evolved, q, in a reaction of 0.10 mole HCl with excess NaOH in aqueous solution is 96 calories. Calculate the number of joules that are evolved. Calculate the number of kilojoules evolved per mole of HCl. Is the reaction endothermic or exothermic? What is ∆H for the reaction in units of kilojoules per mole of HCl? (2 pts) Given the following information, use Hess’s law to calculate the enthalpy change for the decomposition of one mole of acetylene (C2H2) gas into its elements in their standard states. The complete combustion in air of one mole of acetylene gas releases 1299.5 kJ of energy. The standard enthalpy of formation of carbon dioxide gas is -393.5 kJ/mol. The standard enthalpy of formation of liquid water is -285.8 kJ/mol. Look up the standard enthalpy of formation for acetylene gas. How does this compare to what you just calculated for the decomposition of acetylene to its elements? Part 2A: Data Mass of CAL: 4.623 g Mass of the CAL + HCl solution: 20.456 g Mass of the Mg: 0.069 g Temperature of the HCl solution initially: 21.2 C Final temperature of the HCl solution + Mg (highest T): 42.5 C Part 2B: Data Mass of the HCl solution: 16.859 g Mass of the MgO: 0.210 g Temperature of the HCl solution initially: 21.4 C Final temperature of the HCl solution + MgO (highest T): 31.2 C Part 2A. Reaction of Mg with HCl (1 pt) Complete and balance the following reaction: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) (2 pts) Determine q for Reaction 1: -qrxn = mwater·Cwater·∆T + Ccal·∆T This energy calculated, qrxn, is for the total mass of Mg that you used, note the units are J. Use the mass of water, not the mass of Mg here. Show all work here. You can use the equation editor to show your work. (1 pt) Calculate the value in units of kilojoules per mole of Mg by dividing qrxn by moles of Mg used. Show your work here. ∆HA =___ (kJ/mol) Note: the sign for the heat of reaction (∆H) is negative for an exothermic reaction and positive for an endothermic reaction. Part 2B. Reaction of MgO with HCl (1 pt) Write the balanced chemical equation for solid MgO reacting with aqueous HCl. MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l) (2 pts) Calculate the heat of this reaction in the same way as in Part 2A. Show all your work, including simple subtractions. The mass of water is used here, not the mass of MgO. -qrxn = mwater·Cwater·∆T + Ccal·∆T (2 pts) Express the heat evolved in units of kilojoules per mole of MgO by dividing by the moles of MgO used and the conversion factor needed to transform Joules into kilojoules. Show your work. ∆HB=kJ/mole Hess’s Law Calculation (1 pt) Write the formation equation for solid MgO. This is your target equation. (3 pts) Calculate the heat of formation of MgO using the equations A, B, and C from the first page. Use the enthalpy values you determined experimentally for equations A and B, and look up the value for C. Manipulate equations A, B, and C so they add up to the target equation. Reaction ∆Hrxn Target (1 pt) The heat of formation of MgO is -601.8 kJ/mol. If your value is vastly different than this value, you likely did something incorrectly in your calculation. Go back and recheck your steps. Calculate your percent error to the true value. Show work (watch significant figures). Experimental Error Review the video and observations carefully and list two possible sources of experimental error. Calculation errors are not experimental error. Discuss briefly (1 or 2 sentences) the specifics about how each error would affect your value for the heat of formation of magnesium oxide. Do not use words like “throw off” – that is not specific – use words like “larger” or “smaller”. An example might be (after you describe the error): “This error would make my value for the enthalpy of formation of magnesium oxide larger than it should be.” (2pt) Error 1 Description: Specific Impact on Final Result: (2 pt) Error 2 Description: Specific Impact on Final Result:

          Preparatory Questions 
(2 pt) The heat evolved, q, in a reaction of 0.10 mole HCl with excess NaOH in aqueous solution is 96 calories.
Calculate the number of joules that are evolved.
Calculate the number of kilojoules evolved per mole of HCl.
Is the reaction endothermic or exothermic?
What is ∆H for the reaction in units of kilojoules per mole of HCl?

(2 pts) Given the following information, use Hess’s law to calculate the enthalpy change for the decomposition of one mole of acetylene (C2H2) gas into its elements in their standard states.
The complete combustion in air of one mole of acetylene gas releases 1299.5 kJ of energy.
The standard enthalpy of formation of carbon dioxide gas is -393.5 kJ/mol.
The standard enthalpy of formation of liquid water is -285.8 kJ/mol.
Look up the standard enthalpy of formation for acetylene gas. How does this compare to what you just calculated for the decomposition of acetylene to its elements?

Part 2A: Data
Mass of CAL: 4.623 g
Mass of the CAL + HCl solution: 20.456 g
Mass of the Mg: 0.069 g
Temperature of the HCl solution initially: 21.2 C
Final temperature of the HCl solution + Mg (highest T): 42.5 C

Part 2B: Data
Mass of the HCl solution: 16.859 g
Mass of the MgO: 0.210 g
Temperature of the HCl solution initially: 21.4 C
Final temperature of the HCl solution + MgO (highest T): 31.2 C

Part 2A. Reaction of Mg with HCl
(1 pt) Complete and balance the following reaction:
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)   

(2 pts) Determine q for Reaction 1:
-qrxn = mwater·Cwater·∆T + Ccal·∆T   
This energy calculated, qrxn, is for the total mass of Mg that you used, note the units are J. Use the mass of water, not the mass of Mg here. Show all work here. You can use the equation editor to show your work.

(1 pt) Calculate the value in units of kilojoules per mole of Mg by dividing qrxn by moles of Mg used. Show your work here.
∆HA =___________ (kJ/mol)
Note: the sign for the heat of reaction (∆H) is negative for an exothermic reaction and positive for an endothermic reaction.
         
Part 2B. Reaction of MgO with HCl
(1 pt) Write the balanced chemical equation for solid MgO reacting with aqueous HCl.
MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)

(2 pts) Calculate the heat of this reaction in the same way as in Part 2A. Show all your work, including simple subtractions. The mass of water is used here, not the mass of MgO.
-qrxn = mwater·Cwater·∆T + Ccal·∆T   
    
(2 pts) Express the heat evolved in units of kilojoules per mole of MgO by dividing by the moles of MgO used and the conversion factor needed to transform Joules into kilojoules. Show your work.
∆HB=________kJ/mole

Hess’s Law Calculation
(1 pt) Write the formation equation for solid MgO. This is your target equation.

(3 pts) Calculate the heat of formation of MgO using the equations A, B, and C from the first page. Use the enthalpy values you determined experimentally for equations A and B, and look up the value for C. Manipulate equations A, B, and C so they add up to the target equation. 
Reaction
∆Hrxn
Target

(1 pt) The heat of formation of MgO is -601.8 kJ/mol. If your value is vastly different than this value, you likely did something incorrectly in your calculation. Go back and recheck your steps. Calculate your percent error to the true value. Show work (watch significant figures).

Experimental Error
Review the video and observations carefully and list two possible sources of experimental error. Calculation errors are not experimental error. Discuss briefly (1 or 2 sentences) the specifics about how each error would affect your value for the heat of formation of magnesium oxide. Do not use words like “throw off” – that is not specific – use words like “larger” or “smaller”. An example might be (after you describe the error): “This error would make my value for the enthalpy of formation of magnesium oxide larger than it should be.” 

(2pt) Error 1
Description:
Specific Impact on Final Result:

(2 pt) Error 2
Description:
Specific Impact on Final Result:

Added by Ronald G.

Chemistry: Structure and Properties

Nivaldo Tro 2nd Edition

Instant Answer

Solved by Expert Federico Castro

Step 1

Given: Mass of water (mwater) = 20.456 g - 4.623 g = 15.833 g Specific heat capacity of water (Cwater) = 4.184 J/g°C Change in temperature (∆T) = 42.5°C - 21.2°C = 21.3°C Mass of Mg = 0.069 g Molar mass of Mg = 24.305 g/mol We can use the formula q = mwater * Show more…

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Preparatory Questions (2 pt) The heat evolved, q, in a reaction of 0.10 mole HCl with excess NaOH in aqueous solution is 96 calories. Calculate the number of joules that are evolved. Calculate the number of kilojoules evolved per mole of HCl. Is the reaction endothermic or exothermic? What is ∆H for the reaction in units of kilojoules per mole of HCl? (2 pts) Given the following information, use Hess’s law to calculate the enthalpy change for the decomposition of one mole of acetylene (C2H2) gas into its elements in their standard states. The complete combustion in air of one mole of acetylene gas releases 1299.5 kJ of energy. The standard enthalpy of formation of carbon dioxide gas is -393.5 kJ/mol. The standard enthalpy of formation of liquid water is -285.8 kJ/mol. Look up the standard enthalpy of formation for acetylene gas. How does this compare to what you just calculated for the decomposition of acetylene to its elements? Part 2A: Data Mass of CAL: 4.623 g Mass of the CAL + HCl solution: 20.456 g Mass of the Mg: 0.069 g Temperature of the HCl solution initially: 21.2 C Final temperature of the HCl solution + Mg (highest T): 42.5 C Part 2B: Data Mass of the HCl solution: 16.859 g Mass of the MgO: 0.210 g Temperature of the HCl solution initially: 21.4 C Final temperature of the HCl solution + MgO (highest T): 31.2 C Part 2A. Reaction of Mg with HCl (1 pt) Complete and balance the following reaction: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) (2 pts) Determine q for Reaction 1: -qrxn = mwater·Cwater·∆T + Ccal·∆T This energy calculated, qrxn, is for the total mass of Mg that you used, note the units are J. Use the mass of water, not the mass of Mg here. Show all work here. You can use the equation editor to show your work. (1 pt) Calculate the value in units of kilojoules per mole of Mg by dividing qrxn by moles of Mg used. Show your work here. ∆HA =___________ (kJ/mol) Note: the sign for the heat of reaction (∆H) is negative for an exothermic reaction and positive for an endothermic reaction. Part 2B. Reaction of MgO with HCl (1 pt) Write the balanced chemical equation for solid MgO reacting with aqueous HCl. MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l) (2 pts) Calculate the heat of this reaction in the same way as in Part 2A. Show all your work, including simple subtractions. The mass of water is used here, not the mass of MgO. -qrxn = mwater·Cwater·∆T + Ccal·∆T (2 pts) Express the heat evolved in units of kilojoules per mole of MgO by dividing by the moles of MgO used and the conversion factor needed to transform Joules into kilojoules. Show your work. ∆HB=________kJ/mole Hess’s Law Calculation (1 pt) Write the formation equation for solid MgO. This is your target equation. (3 pts) Calculate the heat of formation of MgO using the equations A, B, and C from the first page. Use the enthalpy values you determined experimentally for equations A and B, and look up the value for C. Manipulate equations A, B, and C so they add up to the target equation. Reaction ∆Hrxn Target (1 pt) The heat of formation of MgO is -601.8 kJ/mol. If your value is vastly different than this value, you likely did something incorrectly in your calculation. Go back and recheck your steps. Calculate your percent error to the true value. Show work (watch significant figures). Experimental Error Review the video and observations carefully and list two possible sources of experimental error. Calculation errors are not experimental error. Discuss briefly (1 or 2 sentences) the specifics about how each error would affect your value for the heat of formation of magnesium oxide. Do not use words like “throw off” – that is not specific – use words like “larger” or “smaller”. An example might be (after you describe the error): “This error would make my value for the enthalpy of formation of magnesium oxide larger than it should be.” (2pt) Error 1 Description: Specific Impact on Final Result: (2 pt) Error 2 Description: Specific Impact on Final Result: