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Calorimetry Lab - Enthalpy Change of a Chemical Reaction

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Procedure:

1. Take a calorimeter from the glassware shelf and place it on the workbench.

2. Take a balance from the tools shelf and drop it on the calorimeter. Record the mass of the empty calorimeter.

3. Take a thermometer from the tools shelf and drop it onto the calorimeter. Record the temperature of the calorimeter.

4. Add 50 mL of 1.0M hydrochloric acid (HCl) to the calorimeter.

5. Add .15g of magnesium (Mg) to the calorimeter.

6. Immediately measure and record the maximum temperature displayed by the thermometer in the calorimeter.

7. Measure and record the mass of the calorimeter and its contents.

8. Repeat the experiment with a new calorimeter, using 50 mL of HCl and .25g of magnesium. Record the maximum temperature displayed by the thermometer in the calorimeter.

9. Repeat the experiment with a new calorimeter, using 50 mL of HCl and .35g of magnesium. Record the maximum temperature displayed by the thermometer in the calorimeter.

Questions:
1. Record the following for each of the three experiments:
(a) Mass of the empty calorimeter (g): ?
(b) Initial temperature in the calorimeter (C): ?
(c) Maximum temperature in the calorimeter from the reaction (C): ?
(d) Calculate deltaT as Tmaximum - Tinitial (C): ?
(e) Mass of the calorimeter and its contents after the reaction (g): ?
(f) Calculate the mass of the contents of the calorimeter (g): ?
(g) Calculate the moles of Mg reacted (MW=24.305 g/mole): ?

2. Calculate the heat released into the solution for the 3 reactions, according to: q(reaction) = Ccal * Delta T + mass(contents) * Cp (contents) * deltaT

(If you have not measured the calorimeter constant yet, assume that it is zero for this experiment.)

3. Find the molar heat of reaction for each experiment in units of Joules/(mole of Mg) by dividing the heat of reaction by the moles of Mg used.

4. Calculate and record the average molar heat of reaction from the three results.

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The Enthalpy Change of a Chemical Reaction

The following are the givens from the experiment:
Experiment 1: Measuring the Calorimeter Constant
Temperature of the Calorimeter = 21.5C
Temperature of Calorimeter after adding the water from the flask from bath= 39.2C

Experiment 2: Enthalpy Change of a Chemical Reaction (3 Trials)

Trial #1
Mass of empty Caloriometer = 18.600g
Temperature of empty Calorimeter = 21.5C
After 50mL of HCl & 0.15g of (Mg) added Max temp= 35.0C
Mass of Calorimeter = 68.738g

Trial #2
Mass of empty Caloriometer = 18.600g
Temperature of empty Calorimeter = 21.5C
After 50mL of HCl & 0.25g of (Mg) added Max temp= 44.0C
Mass of Calorimeter = 68.829g

Trial #3
Mass of empty Caloriometer = 18.600g
Temperature of empty Calorimeter = 21.5C
After 50mL of HCl & 0.35g of (Mg) added Max temp= 52.9C
Mass of Calorimeter = 68.921g

I'm totally lost on this lab so there are several questions I need answered from the above information. They are listed below.

Experiment #1 I believe A&B are correct I needC, & 2,3,4,5
A. Initial temperature in the calorimeter (C)=21.5C
B. Maximum temperature in the calorimeter from the reaction (C): = 39.2C
C. Calculate deltaT by subtracting (b) from (c)
deltaT = Tinitial (C):

2. What was the initial heat energy before mixing the cold and hot water? To calculate this you need to use the formula :
Qinitial = m1*Cp*T(of the hot water) + m2*Cp*T(of the cold water)
where Q is the heat energy, m is the mass , Cp is the specific heat of water 4.184 J/g*C, and T is the temperature.

3. What was the final heat energy after mixing the cold and hot water? To calculate this you need to use the formula :
Qfinal = (m1+m2) * Cp * Tfinal

4. What is the heat energy of the calorimeter? You can calculate the calorimeter heat energy as the difference between the initial and final heat energies.Choose the closest answer.

5. What is the calorimeter constant? You can calculate the calorimeter constant, Ccal, per degree change of the calorimeter by taking the calorimeter heat energy and dividing it by the temperature change undergone by the calorimeter:

Experiment #2

1. Record the following for each of the three trials: I have answers for A-F for each trial are they correct?

Trial 1 ( I think A,B C D,E,& F are correct if so I need G )
A) Mass of the empty calorimeter (g):= 18.600g
B) Initial temperature in the calorimeter (C):=21.5C
C) Maximum temperature in the calorimeter from the reaction (C):=35.0C
D) Calculate deltaT by subtracting (b) from (c)
deltaT = Tmaximum - Tinitial (C): = 13.5C
E) Mass of the calorimeter and its contents after the reaction (g): = 68.738g
F) Calculate the mass of the contents of the calorimeter (g): e - a = 50.138g
G) Calculate the moles of Mg reacted (MW=24.305 g/mole): =

Trial 2 ( I think A,B C D,E,& F are correct if so I need G )
A) Mass of the empty calorimeter (g):= 18.600g
B) Initial temperature in the calorimeter (C):=21.5C
C) Maximum temperature in the calorimeter from the reaction (C):=44.0C
D) Calculate deltaT by subtracting (b) from (c)
deltaT = Tmaximum - Tinitial (C): = 22.5C
E) Mass of the calorimeter and its contents after the reaction (g): 68.829g
F) Calculate the mass of the contents of the calorimeter (g): e - a =50.229g
G) Calculate the moles of Mg reacted (MW=24.305 g/mole):

Trial 3 ( I think A,B C D,E,& F are correct if so I need G )
A) Mass of the empty calorimeter (g):= 18.600g
B) Initial temperature in the calorimeter (C):=21.5C
C) Maximum temperature in the calorimeter from the reaction (C):=59.2C
D) Calculate deltaT by subtracting (b) from (c)
deltaT = Tmaximum - Tinitial (C): =37.7C
E) Mass of the calorimeter and its contents after the reaction (g): =68.921g
F) Calculate the mass of the contents of the calorimeter (g): e - a = 50.321g
G) Calculate the moles of Mg reacted (MW=24.305 g/mole):

2. Calculate the heat released into the solution for the 3 reactions, according to:
ᅠᅠᅠq(reaction)ᅠ=ᅠCcal * Delta T + mass(contents) * Cp (contents) * deltaT
Cp is the specific heat (assume 4.18 J/goC)

A) Trial 1(J) =
B) Trial 2 (J)=
C) Trial 3 (J) =

3. Find the molar heat of reaction for each experiment in units of KiloJoules / (mole of Mg) by dividing the heat of reaction (converted to KJ by dividing by 1000) by the moles of Mg used.

A) Trial 1 KJ/mol =
B) Trial 2 KJ/mol =
C) Trial 3 KJ/mol =

4. Calculate and record the average molar heat of reaction from the three results.

Background
When an exothermic reaction takes place in a container, heat is released and the temperature of the container and its contents increases. The contents of the container include: the reaction products and typically a solvent (such as water). The measurement of heat transfer under controlled conditions is called calorimetry (from the unit of heat energy, the calorie), and a container used to measure heat transfer is called a calorimeter. The calorimeter prevents heat transfer to or from the surroundings, thereby isolating the system being measured.

When a reaction occurs in a relatively large amount of water, we can assume that the water is the sole medium absorbing the heat of reaction and then calculate the heat of reaction by measuring the temperature change of the water, according to the following relationships:

Q(water) = mass(water) × Cp(water) × ∆T(water) = Q(reaction)

where Cp(water) is the specific heat of water, 4.18 J/g _C, and ∆T (also known as deltaT) is the difference between the initial and final temperatures.

The absorption of heat by the calorimeter should also be taken into account and added to the heat absorbed by the water. The steps to calibrate the calorimeter as to obtain the calorimeter constant will be explained at the beginning of the lab. Once this constant has been obtained, the total heat of the reaction is given by:

Q = Ccal × ∆T + mass(water) × Cp(water) × ∆T
In the current experiment you will measure the heat generated by the reaction:

Mg(s) + 2HCl(aq) → Mg+2 (aq) + 2Cl-(aq) + H2(g)

The heat of the reaction is expressed in units of Joules per moles of reactant; in this case, you will find the heat of reaction per moles of Mg.

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