Thermal Energy -Physics
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Steam passes into a jug to warm up some cold water. In this question, you may ignore any heating of atmosphere.
Pure steam enters at 100deg cel and jug initially contains 500g of water at 20 deg cels. Eventually water in the jug reachers a temperature of 100 deg cel. Specific heat capacity of water is 4.20J/g deg cel and specific latent heat of vaporisation of water is 2250J/g.
1calculate energy needed to warm 500g of water from 20 deg cel to 100 deg cel.
2. calculate final mass of water in jug when temperature has reached 100 deg cel.
For the first question, do i just find the energy using the S. heat capacity method or do i need to include the s. latent of of vaporisation method? I don't think we needa find the energy for the latter since there's no change in state anyway.
as for the second question do i equate the energy(FOUND USING S.HEAT CAPACITY METHOD) with the s. latent heat of vaporisation? i got 74.....g. then do i add on to the initial 500g of water? by the way, why does water in jug increase anyway?
ADAPTED FROM TYS (N2000 P2 Q5)
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1. Q = mcΔT = (500g)(4.2Jg-¹K-¹)(80K) = 168kJ
2. Energy put in to heat water = Energy released by condensation of steam
Let m be the final mass of water in grams.
Q = (m-500)L
m-500 = Q/L = 168kJ/(2.25kJg-¹) = 74.7g
∴ m = 574.7g -
For the first question, do i just find the energy using the S. heat capacity method or do i need to include the s. latent of of vaporisation method? I don't think we needa find the energy for the latter since there's no change in state anyway.
Yes, since there is no change of state required, latent heat is not required here.
In this question, steam gets converted to 100ºC water. Only the latent energy of vapourisation is used to heat up the 20ºC water already in that system to 100ºC, so once steam gets converted to water of 100ºC, the end product for steam is achieved.as for the second question do i equate the energy(FOUND USING S.HEAT CAPACITY METHOD) with the s. latent heat of vaporisation? i got 74.....g. then do i add on to the initial 500g of water? by the way, why does water in jug increase anyway?
Simply because steam gets converted to 100ºC water and joins the water already present in that system. You will need to add in the initial 500g since it is part of the final mass of water.
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That's a lot of help. Thanks!
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No prob. (: