In an aluminum calorimeter, 25.00 g of I2 was burned in excess H2 to form HI. From the data below, establish the molar heat of reaction and write a thermochemical reaction.

Question

In an aluminum calorimeter, 25.00 g of I2 was burned in excess H2 to form HI. From the data below, establish the molar heat of reaction and write a thermochemical reaction.

Data:
Mass I2 25.00 g
Mass Al 70.00 g
Specific heat Al 0.900 J/gC
Volume water 100.0 mL
Initial temperature 34.6C
Final temperature 23.8C

Answer 1

I2+...? 2HI

so for each mole of I2 burned, two moles of HI is achieved.

molesI2=25/127

Heatfrom I2 + HeatgainedbyAl + heatgainedwater=0
HeatfromI2+70(.900)(23.8-34.6) +200*4.19*(23.8-34.6)=0
solve for HeatfromI2
molareatofrecton for I2=heatfromI2 /2
that is the heat per mole of HI formed

Answer 2

To determine the molar heat of reaction and write a thermochemical reaction, we can follow these steps:

1. Calculate the heat absorbed or released by the water:

The heat absorbed or released by the water can be calculated using the formula:

q = m × C × ΔT

Where:
q = heat absorbed or released (in joules)
m = mass of water (in grams)
C = specific heat of water (4.18 J/g°C)
ΔT = change in temperature (final temperature - initial temperature)

Substituting the given values:
m = volume of water × density of water (density of water = 1 g/mL)
m = 100.0 g/mL × 1 g/mL = 100 g

C = 4.18 J/g°C
ΔT = 23.8°C - 34.6°C = -10.8°C (negative since temperature decreased)

q = 100 g × 4.18 J/g°C × (-10.8°C)
q = - 4531.2 J (Joules)
(Note: The negative sign indicates heat released by the water.)

2. Calculate the heat absorbed or released by the aluminum calorimeter:

The heat absorbed or released by the aluminum calorimeter can be calculated using the formula:

q = m × C × ΔT

Where:
q = heat absorbed or released (in joules)
m = mass of aluminum (in grams)
C = specific heat of aluminum (0.900 J/g°C)
ΔT = change in temperature (final temperature - initial temperature)

Substituting the given values:
m = 70.00 g
C = 0.900 J/g°C
ΔT = 23.8°C - 34.6°C = -10.8°C (negative since temperature decreased)

q = 70.00 g × 0.900 J/g°C × (-10.8°C)
q = - 680.4 J (Joules)
(Note: The negative sign indicates heat released by the aluminum calorimeter.)

3. Calculate the total heat absorbed or released by the reaction:

The total heat absorbed or released by the reaction can be obtained by summing the heat absorbed or released by the water and the aluminum calorimeter:

q_total = q_water + q_aluminum

q_total = (-4531.2 J) + (-680.4 J)
q_total = -5211.6 J (Joules)
(Note: The negative sign indicates that the overall reaction releases heat.)

4. Convert grams of I2 to moles:

To calculate the molar heat of reaction, we need to convert the grams of I2 to moles. The molar mass of I2 is 253.8 g/mol.

moles of I2 = mass of I2 / molar mass of I2
moles of I2 = 25.00 g / 253.8 g/mol
moles of I2 = 0.09857 mol

5. Calculate the molar heat of reaction:

To determine the molar heat of reaction, we divide the total heat absorbed or released by the reaction by the number of moles of I2.

ΔH = q_total / moles of I2
ΔH = -5211.6 J / 0.09857 mol
ΔH = -52,905 J/mol (Joules per mole)

6. Write the thermochemical reaction:

The thermochemical reaction can be written as:

I2 + 2H2 -> 2HI

ΔH = -52,905 J/mol (heat is released)