Absorption Of Heat; water and steam thermodynamics

You have used kJ instead of J for the heat of vaporisation. Also, the specific heat of water should be in J/kgK, not J/kg.oC. In summary, steam at 120 oC is passed into 0.60 kg of water at 20 oC, and the total mass of water is brought to a boil at 100 oC. The mass of condensed steam is 87g, or 0.087 kg. This can be found by setting the heat gained by the water equal to the heat lost by the steam being cooled and condensed. Using the correct units for the heat of vaporisation and specific heat, the mass of condensed steam is found to be 0.087 kg.
  • #1
K29
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Homework Statement


Steam initially at 120 oC is passed into 0.60 kg of water initially at 20 o C, and the total mass of water is just brought to the boil at 100C

What is the mass of steam that has condensed? Ignore the thermal capacity of the container and heat losses.



Homework Equations



Q = cm(T2-T1) heat = specific heat * mass * change in temperature
Q = Lm heat = heat of Vaporisation or Fusion * mass
Heat of vaporisation of water is 2260 kJ/kg
Specific heat of water is 4200 J/kg.oC
Specific heat of steam is 2100 J/kg.oC


The Attempt at a Solution


Qgained by water being heated = Qlost by steam being cooled + Q Lost by steam being condensed

cmw(T2-T1) = cmstot(T2-T1) +Lmscondensed

Unfortunately I can't seem to get rid of mstot. It is not given and I need to either work it out or find another equation. Help!
If it helps, the final answer should be 87g
 
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  • #2
If the problem can't be solved otherwise, why not assume that all the steam condensed?
 
  • #3
I have tried this and get
|cmw(T2-T1)| = |cms(T2-T1)| +|Lms|
|4200 * 0.6 (100-20)| = |2100 * ms(100-120)| + |2260ms|
|201600|= |-42000ms|+|2260ms|
201600 = 42000ms+2260ms
201600=44260ms
ms=4.55 kg

As I said above the answer given in the notes is 87g = 0.087kg :(
 
  • #4
Check your units.
 

1. What is the definition of absorption of heat?

The absorption of heat refers to the process by which a substance or object takes in heat energy from its surroundings, causing an increase in its temperature.

2. How does water absorb heat?

Water absorbs heat through the process of convection, where warmer water rises to the surface and cooler water sinks. This allows for the transfer of heat throughout the water, keeping its temperature relatively constant.

3. How does the absorption of heat affect the state of water?

The absorption of heat can cause water to change states, from solid to liquid to gas. When heat is absorbed, the molecules in water gain energy and move faster, causing ice to melt into liquid water and liquid water to boil into steam.

4. What is the role of steam in thermodynamics?

Steam plays a crucial role in thermodynamics as it is the gaseous phase of water and has a high capacity for heat absorption. Steam is widely used in power generation and industrial processes for its ability to transfer large amounts of heat energy.

5. How does the absorption of heat impact the environment?

The absorption of heat can have both positive and negative impacts on the environment. On one hand, it helps regulate the Earth's temperature and supports life on our planet. However, excessive absorption of heat, such as through the greenhouse effect, can lead to global warming and negative consequences for the environment.

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