A typical 12v batter can deliver about 7.5 x 10^5 C

[atoreta88]

PROBLEM: A typical 12v battery can deliver about 7.5 x 10^5 C of charge before dying. This is not very much. To get a feel for this calculate the maximum number of kilograms of water (100 degrees celsius) that could be boiled into steam (100degrees celsius) using energy from this battery.

I think I'm supposed to use the formula, E= qv, but I don't know what to do after that.

 

[Phrak]

Using E=qv, your energy will be in units of Joules. How many Joules does it take to raise 1 kilogram of water 1 degree Celcius?

Edit: Oops. After re-reading the question, I see that the intent is to bring liquid water from 100C to vapor at 100C. For this, look up Latent heat of vaporization of water.

 

[atoreta88]

Using E=qv, your energy will be in units of Joules. How many Joules does it take to raise 1 kilogram of water 1 degree Celcius?

Edit: Oops. After re-reading the question, I see that the intent is to bring liquid water from 100C to vapor at 100C. For this, look up Latent heat of vaporization of water.

Thanks for responding. So all I have to do is look up that value for the latent heat of vaporization and that would be my final answer...I don't have to use any formula to calculate anything? I looked up the value and for 100 degrees C, the latent heat is 2260 kj/kg...would that be all?

 

[AJ Bentley]

Read the question carefully, then:-

So what you've got, is that you need 2260kJ of energy to change each kg of boiling water into steam.

How many joules of energy do you have available in the battery?

How does that help you answer the question that was asked.

 

[rwisz]

I would approach this problem by first converting the charge delivered by the battery, 7.5 x 10^5 C, into energy using the formula E= qv. In this case, the voltage (v) is given as 12V, so the energy delivered by the battery would be 9 x 10^6 J (joules).

Next, I would use the specific heat capacity of water, which is 4.186 J/g°C, to calculate the amount of energy needed to raise the temperature of 1 kg of water from 100°C to its boiling point of 100°C. This would be 418.6 kJ (kilojoules).

Since the energy delivered by the battery is 9 x 10^6 J, we can divide this by the energy needed to raise the temperature of 1 kg of water to determine the maximum number of kilograms of water that can be boiled. This would be approximately 21.5 kg of water (9 x 10^6 J / 418.6 kJ = 21.5 kg).

Therefore, using energy from this typical 12V battery, we can boil approximately 21.5 kg of water into steam. This may not seem like a lot, but it is important to keep in mind that a battery's main function is to provide electrical energy, not thermal energy. There are other sources of energy that are more efficient for heating water, such as a stove or a water heater.