Question as follows:
If you combusted 23g of ethanol with an excess of oxygen how much heat would be released or absorbed?
the only thing I've deduced is the chemical reaction:
C2H6O + 302 -> 3H20 + 2C02
I'm not sure how to proceed. I need Q. Not sure which equation to use since there is no temperature. Am I to assume 298K?
No. You find the heat of combustion which is in tables (or you can calculate it), then
q = dHcombustion x (23g/molar mass ethanol)
If you don't have heat combustion tables you can calculate it this way. From your equation above, use
dHfrxn = dH combustion = (n*dHf products) - (n*dHf reactants). The heats of formation are in tables, too, usually in the appendix. CO2 is approx -393.5 kJ/mol (but I don't remember all of these so you must look them up) and H2O is about -285 kJ/mol or so. I don't have the foggiest about ethanol.
To determine the amount of heat released or absorbed in a chemical reaction, you can use the concept of reaction enthalpy (∆H). The reaction enthalpy is the heat change associated with a chemical reaction.
In this case, the reaction you've identified for the combustion of ethanol is correct:
C2H6O + 3O2 -> 2CO2 + 3H2O
To find the heat released or absorbed in this reaction, you need to know the enthalpy change (∆H) of this reaction. The enthalpy change is typically given in units of kJ/mol.
To proceed, you can look up the standard enthalpy change of combustion for ethanol (∆H°comb) in reference tables or online sources. The standard enthalpy change of combustion refers to the enthalpy change when the reaction occurs under a standard set of conditions (usually 298K and 1 atm).
For ethanol, the standard enthalpy change of combustion (∆H°comb) is approximately -1366 kJ/mol. Note that the negative sign indicates that the reaction is exothermic, meaning it releases heat.
To calculate the amount of heat released or absorbed when combusting a known mass of ethanol, you need to convert the mass of ethanol to moles. The molar mass of ethanol (C2H6O) is approximately 46.07 g/mol.
Given that you have 23 g of ethanol, you can calculate the number of moles:
moles of ethanol = mass / molar mass
moles of ethanol = 23 g / 46.07 g/mol ≈ 0.5 mol
Now that you have the number of moles, you can calculate the heat released or absorbed using the following equation:
Q = ∆H x moles of ethanol
Q = -1366 kJ/mol x 0.5 mol ≈ -683 kJ
Hence, approximately -683 kJ of heat would be released when combusting 23 g of ethanol with an excess of oxygen.
Note: If you want to calculate the heat at a different temperature, you would need to consider the temperature dependence of the enthalpy change (∆H) and use the appropriate equations or temperature corrections.