What mass of LP gas is necessary to heat 1.7 L of water from room temperature (25.0 ∘C) to boiling (100.0 ∘C)? Assume that during heating, 16% of the heat emitted by the LP gas combustion goes to heat the water. The rest is lost as heat to the surroundings.

Respuesta :

Answer:

72.25 g

Explanation:

mass of 1.7 L water = 1.7 x 10⁻³ x 10³ kg

= 1.7 kg

heat required to raise its temperature from 25 degree to 100 degree

= mass x specific heat x rise in temperature

= 1.7 x 4.18 x 10³ x 75 J

= 532.95 kJ

Now calorific value of LP gas = 46.1 x 10⁶J / kg

Let required mass of LP gas be m kg

heat evolved from this amount of gas

=  46.1 x 10⁶ m

Heat utilized in warming water  

= 46.1 x 10⁶ m  x .16 J

So

46.1 x 10⁶ m  x .16  =  532.95 x 10³

7376 x 10³ m = 532.95 x 10³

m = 532.95 / 7376 kg

= 72.25 g

The mass of LP required is  0.0018 g of LP

C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)

ΔH∘rxn= −2044kJ

We know from the question that the volume of water =  1.7 L

Since the density of water is 1 g/L

Mass of water = 1.7 g

Heat capacity of water = 4.18 J/g.∘C

Heat gained by water = mcθ

m = mass of water

c = heat capacity of water

θ = temperature rise of water

H =  1.7 g × 4.18 J/g.∘C × (100.0 ∘C - 25.0 ∘C)

H = 532.95 J

Heat lost by LP = heat gained by water

Recall that only 16% of the heat lost by LP was gained by water so, heat lost by LP = 0.16 × (- 532.95 J) = -85.827 J

1 mole of LP contains 44 g

44 g of LP produces −2044 × 10^3 J of heat

x g of LP produces  -85.827 J

x = 44 g × -85.827 J /−2044 × 10^3 J

x = 0.0018 g of LP

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