A 2.75 g sample of the hydrocarbon acetone, CH3COCH3, is burned in a bomb calorimeter with 975 mL of water, initially at 23.50 degrees celsius. The bomb is constructed of 285.0 g of nickel metal having a specific heat capacity of Cp = 0.826 J/ g degrees C. The final temperature of the bomb and the water after the combustion process increases to 29.55 degrees celsius. calculate the following:
(a)The heat flow at constant volume, qv for this combustion (in kJ/mol).
i know qv = delta E. and that delta E = q + w. but how do i find the work? i know work = force / distance. (i'm sorry if i sound incompetant but i'm struggling because my book gives and example where the work is already given so its not helpful at all.)
(b)The energy released per mole of acetone (in kj/mole).
(c)calculation (b) amounts to the heat of combustion per mole, delta h comb/mole for this compound. Balance the reaction for the complete combustion of acetone, find delta n and then find the value of delta H per mole of acetone (kJ/mole).
i don't know how to even start part (b).
To calculate the heat flow at constant volume (qv), you can use the equation:
qv = ΔE
where ΔE is the change in internal energy of the system. In this case, the system consists of the combustion of acetone and the resulting increase in temperature of the water and bomb calorimeter.
To calculate ΔE, you need to consider the heat transferred (q) and the work done (w). However, in this scenario, the bomb calorimeter is a constant volume system, so no work is done:
w = 0
This means that ΔE = q.
To find q, you can use the equation:
q = mcΔT
where m is the mass of the water and bomb (in grams) and c is the specific heat capacity of the bomb calorimeter and nickel metal.
Given:
Mass of water and bomb (m) = 975 g + 285 g = 1260 g
Specific heat capacity of the nickel metal (c) = 0.826 J/g°C
Change in temperature (ΔT) = final temperature - initial temperature = 29.55°C - 23.50°C = 6.05°C
Now you can calculate q:
q = (1260 g)(0.826 J/g°C)(6.05°C)
q = 6247.53 J
To convert J to kJ, divide by 1000:
qv = 6.25 kJ
Therefore, the heat flow at constant volume for this combustion (a) is 6.25 kJ.
Moving on to part (b), to determine the energy released per mole of acetone, you need to calculate the total moles of acetone that were burned.
Given the molar mass of acetone (M) = 58.08 g/mol, you can calculate the moles of acetone (n) in the sample:
n = mass / molar mass
n = 2.75 g / 58.08 g/mol
n = 0.0473 mol
To find the energy released per mole of acetone, divide the heat flow at constant volume by the number of moles:
Energy released per mole of acetone = qv / n
Energy released per mole of acetone = 6.25 kJ / 0.0473 mol
Now you can calculate the value for (b).
For part (c), the heat of combustion per mole (ΔHcomb/mole) can be determined by balancing the equation for the complete combustion of acetone and calculating the change in moles (Δn).
The balanced equation for the combustion of acetone is:
2CH3COCH3 + 9O2 -> 6CO2 + 8H2O
From the balanced equation, you can see that for every mole of acetone burned, 6 moles of CO2 are produced. So, Δn = -6.
Finally, to find the value of ΔH per mole of acetone (ΔH/mole), divide the energy released per mole of acetone by the change in moles:
ΔH/mole = Energy released per mole of acetone / Δn
Now you can calculate the value for (c) using the given values.
I hope this helps you with your calculations.
To calculate the heat flow at constant volume (qv) for the combustion of acetone, you first need to find the amount of heat transferred during the process (q). In this case, q includes both the heat transferred to the water and the heat absorbed by the bomb.
Now, let's break down the process step by step:
Step 1: Calculate the heat transferred to the water (q_water).
To calculate the heat transferred to the water, you can use the equation:
q_water = m_water * Cp_water * ΔT_water
Where:
- m_water is the mass of water (975 mL) in grams.
- Cp_water is the specific heat capacity of water (approximately 4.18 J/g°C).
- ΔT_water is the change in temperature of the water, which is the final temperature minus the initial temperature.
Step 2: Calculate the heat absorbed by the bomb (q_bomb).
To calculate the heat absorbed by the bomb, you can use the equation:
q_bomb = m_bomb * Cp_bomb * ΔT_bomb
Where:
- m_bomb is the mass of the nickel bomb (285.0 g).
- Cp_bomb is the specific heat capacity of nickel (0.826 J/g°C).
- ΔT_bomb is the change in temperature of the bomb, which is the final temperature minus the initial temperature.
Step 3: Calculate the total heat transferred (q) by summing up q_water and q_bomb.
q = q_water + q_bomb
Step 4: Convert the mass of acetone to moles.
To calculate the energy released per mole of acetone, you need to know the amount of acetone in moles. You can convert the mass of acetone to moles using the molar mass of acetone (58.08 g/mol).
moles of acetone = mass of acetone / molar mass of acetone
Step 5: Calculate the energy released per mole of acetone (in kJ/mol).
To calculate the energy released per mole of acetone, divide the total heat transferred (q) by the moles of acetone.
Energy per mole of acetone = q / moles of acetone
Step 6: Convert the energy released per mole of acetone to kJ.
I hope this helps you solve parts (a) and (b) of the problem! If you have any further questions, feel free to ask.