[nelly23]

LP gas burns according to the following exothermic reaction: C_3H_8 (g) + 5O_2(g)> 3CO_2 (g) +4H2O   (water) : the change in the enthalpy of the rxn is -2044 kJ. What mass of LP gas is necessary to heat 1.7  L of water from room temperature (25.0 degrees celcius ) to boiling (100.0 degrees celcius)? Assume  that during heating, 15% of the heat emitted by the LP gas combustion goes to heat the water. The rest is lost as heat to the surroundings.

[Yggdrasil]

Please read the Forum Rules.  You should that show you've at least attempted to answer the problem before we will help you.

What part of the problem is troubling you specifically?  Can you calculate how much heat is needed to heat 1.7L of water from 25degC to 100 degC?

[nj_bartel]

LP gas burns according to the following exothermic reaction: C_3H_8 (g) + 5O_2(g)> 3CO_2 (g) +4H2O   (water) : the change in the enthalpy of the rxn is -2044 kJ. What mass of LP gas is necessary to heat 1.7  L of water from room temperature (25.0 degrees celcius ) to boiling (100.0 degrees celcius)? Assume  that during heating, 15% of the heat emitted by the LP gas combustion goes to heat the water. The rest is lost as heat to the surroundings.

You're going to need to find an equation linking the specific heat of water (it's a constant, 1cal/[(gram)(^oC)], the change in the temperature of the water, the amount of water, the amount of C₃H₈, and the heat release of the rxn that contributes to heating the water.

Hint: the specific heat of water I gave does not have the proper units; you must determine what form the amount of C₃H₈ and H₂O is to be in, and the correct units for temperature.

Note: This is not a 100% efficient heating process.


edit: If my post gave away too much, please let me know, Yggdrasil.