Physics

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Please Help! I am having difficulties grasping these concepts. Explain please!

1. How much heat energy is required to change 500 grams of water at 100 degrees Celsius to steam at 100 degrees Celsius?

2. How much energy is lost if 7kg of water is cooled from 46 degrees Celsius to 2 degrees Celsius?

3. How much energy is gained when a 300g piece of ice at -25 degrees Celsius is changed to steam at 155 degrees Celsius?

4. A 30 metre steel column in a building is constructed at 20 degrees Celsius. What will the length of the column be at -43 degrees Celsius?

5. An unknown amount of water at 100 degrees Celsius is mixed with 200g of water at 20 degrees Celsius. The final temperature of the solution is 30 degrees Celsius. what is the unknown amount of water?

  • Physics -

    heat changing water to vapor=mass*Hv
    heat changing solid to liquid=mass*hf
    heat changing temperature=mass*specificheat*changeInTemp

    so number three...
    heat to heat ice from -25to zero: m*specificheatice*(0--25)
    heat to melt ice: m*Hffor ice look it up
    Heat to warm water from zero to 100C=m*specheatwater*(100-0)
    heat to vaporize water: mass*Hv (look it up)
    heat to heat steam t0 155: mass(specifheatsteam)(155-100)

    then add the heats.

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