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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: KisaP on May 20, 2020, 11:19:59 PM

Title: energy calculations
Post by: KisaP on May 20, 2020, 11:19:59 PM

Answer the following questions for the balanced reaction.
CO2 (g)     +      2H2O(l)          -->      CH4 (g)     +      2O2 (g)             ΔHrxn= +213 kcal
If 341 kcal of energy was consumed what mass of CO2 was used?

Answer the following questions for the balanced reaction.
CO2 (g)     +      2H2O(l)          -->       CH4 (g)     +      2O2 (g)             ΔHrxn= +213 kcal
If 54.65 g CH4 is produced what amount of energy was used?

Answer the following questions for the balanced reaction.
CO2 (g)     +      2H2O(l)          -->      CH4 (g)     +      2O2 (g)             ΔHrxn= +213 kcal
If 306 kcal of energy was consumed what mass of H2O was used?

- To begin a 0.230g sample of Argon (Ar) gas is at 25.0ᵒC in a 0.253 L tank.
- The gas is then heated and the temp increased until the pressure inside rises to 1.55 atm.
Given the specific heat of Argon is SAr = 0.124 cal/gᵒC find the energy (cal) that went into the gas.

If 1.2g of 100.0C steam begins to condense on a container of liquid water at 25.0C and they eventually reach the same temperature of 46.7C what was the mass of liquid water in the container?
*Assume all heat from the steam cooling goes into the liquid water.*

If an 3.6 g piece of water ice at -15C has 560 calories (enough to liquefy it) added to it what would end temperature be?


I have done these problems 6 times and gotten them all wrong and I really do not understand how to do them. My assignment is due at 11:59 pm tonight :( and i need help with this study guide! ??? please please help if you can :-\

Title: Re: energy calculations
Post by: Enthalpy on May 21, 2020, 05:10:28 AM

Please show us your attempts, so we can comment them. Try to separate the questions, as apparently they're independent.

Sidenote 1: the first reaction won't happen in this direction, or over very indirect paths. It doesn't prevent making computations.

Sidenote 2: cal is a deprecated unit. J is now standard. But you must know cal to read older data and publications.

Sidenote 3: gasses have two usual heat capacities: at constant volume and at constant pressure. Check every time which one fits.

Sidenote 4 : °C measures only temperatures relative to melting ice. The standard unit for temperature differences is K, for instance in J/mol/K.