What is the enthalpy change (in kJ) for burning 49.0 g of methyl alcohol?
I tried this question and got the wrong answer of 1047.74.
A gas is compressed from 73.7 L to 1.9 L at 0.70 atmospheres? In addition a total of 4400 J of heat are gained from warmer surroundings. What is the change in internal energy in kJ?
I have a general idea of how to do this, but I tried and got -2851.8, which isn't right.
Any help is appreciated!
2CH3OH + 3O2 ==> 2CO2 + 4H2O
dHrxn in kJ = (n*dHf products( - (n*dHf reactants)
dHrxn x (49g/2*molar mass CH3OH) = ?kJ.
To calculate the enthalpy change for burning methyl alcohol, you need to use the equation:
ΔH = q / n
Where:
ΔH is the enthalpy change (in kJ),
q is the heat released or gained during the reaction (in J),
and n is the number of moles of the substance involved in the reaction.
To calculate the number of moles, use the formula:
n = mass / molar mass
The molar mass of methyl alcohol (CH3OH) is approximately 32.04 g/mol.
Now, let's calculate the enthalpy change for burning 49.0 g of methyl alcohol:
Step 1: Calculate the number of moles:
n = 49.0 g / 32.04 g/mol ≈ 1.5294 mol
Step 2: Calculate the enthalpy change:
ΔH = q / n
Since the question does not provide the heat released or gained (q), it seems that additional information is needed to solve this problem correctly.
To determine the enthalpy change for burning methyl alcohol, you would need to know the balanced chemical equation for the combustion of methyl alcohol and the molar enthalpy of combustion, typically given in kJ/mol.
First, write the balanced chemical equation for the combustion of methyl alcohol (CH3OH):
2CH3OH + 3O2 -> 2CO2 + 4H2O
Based on this equation, you can see that for every 2 moles of methyl alcohol burned, it produces 2 moles of carbon dioxide (CO2) and 4 moles of water (H2O).
Next, calculate the molar mass of methyl alcohol (CH3OH). The molar mass is the sum of the atomic masses of each element in the compound:
Molar mass of C = 12.01 g/mol
Molar mass of H = 1.01 g/mol
Molar mass of O = 16.00 g/mol
Molar mass of CH3OH = (12.01 x 1) + (1.01 x 4) + 16.00 = 32.04 g/mol
Now, determine the number of moles of methyl alcohol in 49.0 g:
moles of CH3OH = mass / molar mass = 49.0 g / 32.04 g/mol
Calculate the value:
moles of CH3OH = 1.5307 mol
Since the balanced equation shows that 2 moles of CH3OH produce a certain amount of energy (enthalpy change), you need to calculate the enthalpy change for 1.5307 moles:
enthalpy change (kJ) = (1047.74 kJ/mol) x (1.5307 mol)
Calculate the value:
enthalpy change = 1606.61 kJ
Therefore, the enthalpy change for burning 49.0 g of methyl alcohol is 1606.61 kJ.
Now, let's move on to the second question about the change in internal energy.
To calculate the change in internal energy, you need to use the first law of thermodynamics, which states that:
Change in internal energy (ΔU) = q + w
Where ΔU is the change in internal energy, q is the heat added or released, and w is the work done on or by the system.
In this case, you are given the heat gained (q) as 4400 J. However, it is important to make sure that the units are consistent. Since the final answer is required in kJ, you should convert 4400 J to kJ:
4400 J = 4.4 kJ
As for the work done (w), it can be calculated using the equation:
Work done (w) = - PΔV
Where P is the pressure and ΔV is the change in volume.
In this case, the pressure P is given as 0.70 atmospheres, and the change in volume ΔV can be calculated by subtracting the initial volume from the final volume:
ΔV = 73.7 L - 1.9 L = 71.8 L
Remember to convert the volume from liters to meters cubed:
1 L = 0.001 m^3
ΔV = 71.8 L x 0.001 m^3/L = 0.0718 m^3
Now, substitute the values into the equation to calculate the work done:
w = - PΔV = - (0.70 atm) x (0.0718 m^3)
However, we need to convert atmospheres to joules, since the unit of work is joules.
1 atm = 101.325 J
w = - (0.70 atm) x (0.0718 m^3) x (101.325 J/atm)
Calculate the value:
w = - 726.975 J
Now, you can calculate the change in internal energy using the first law of thermodynamics equation:
ΔU = q + w
Substitute the values:
ΔU = 4.4 kJ + (-726.975 J)
Since the units need to be consistent, convert -726.975 J to kJ:
-726.975 J = -0.726975 kJ
Calculate the value:
ΔU = 4.4 kJ - 0.726975 kJ
ΔU = 3.673025 kJ
Therefore, the change in internal energy is approximately 3.67 kJ.