Calculate Heat Required to Raise Water Temperature: 5kg, 60° to Boiling Point

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In summary, the correct answer to the question is b) 2 x 10^5. The correct calculation is Q = 5 kg * 4186 J/(kg C) * 40 C = 837,200 J. Converting to calories, the answer is 200,095 cal = 2 x 10^5. The discrepancy with the answer a) given in the original question is due to a mistake in the conversion of units.
  • #1
jack1234
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How many calories of heat are required to raise the temperature of 5 kg of water from 60° to the boiling point? Select the correct answer.

a. 4.2 x 10^5
b. 2 x 10^5
c. 7.5 x 10^4
d. 18 x 10^5
e. 420

The answer is a, but what I calculate
Q=mcdeltaT
=5*4186*1
=20930
is b, am I doing anything wrong?
 
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  • #2
What is the boiling point of water?
What is Delta T ?
 
  • #3
Em, i suppose you mean [tex] Q=5*4186*10 [/tex] and in that you included your division by four to change the joules into calories.

I can't see anything wrong anyways, unless it wanted you to include the latent heat of vaporization into the formula, though I doubt that would change your answer by much.

I may be wrong too though..
 
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  • #4
O...I think the answer in original question is not correct, it should be
it should be
Q=5000g * 1 J/(calories*celcius) * 40 celcius
=20000J

However the answer is still b though, what is the problem?
 
  • #5
You're quite close, but I have the feeling you're mixing up your units.
Here's the correct calculation (note how I leave in the units and let them cancel at the end).

Q = m * C * dT
= 5 kg * 4186 J/(kg C) * 40 C
= 837,200 J.

Now taking 1 cal = 4.184 J (which seems to be the accepted value),
Q = 200,095 cal = 2 x 105
in the correct number of significant digits.
So the answer is b) -- if it says it's a) then it is wrong :smile:
 

1. How do I calculate the heat required to raise the temperature of 5kg of water from 60° to boiling point?

To calculate the heat required, you will need to use the specific heat capacity of water, which is 4.184 J/g°C. Multiply this by the mass of water (5kg) and the change in temperature (boiling point - 60°). This will give you the total heat required in joules (J).

2. What is the specific heat capacity of water?

The specific heat capacity of water is 4.184 J/g°C. This means that it takes 4.184 joules of energy to raise the temperature of 1 gram of water by 1 degree Celsius.

3. Can I use a different unit of mass and temperature for this calculation?

Yes, as long as the units are consistent. For example, if you use kilograms (kg) for mass, you should use degrees Celsius (°C) for temperature.

4. What is the boiling point of water?

The boiling point of water is 100°C or 212°F at standard atmospheric pressure.

5. How accurate is this calculation for real-life scenarios?

This calculation provides an estimate of the heat required to raise the temperature of water. Factors such as the container used, the starting temperature of the water, and heat loss to the surroundings may affect the actual amount of heat needed in a real-life scenario.

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