How would one determine how much energy is given of by one of those hand warmers?

Question

I know that iron reacts with the oxygen in the air but where do i go from that?

Answer 1

You could place the hand warmer in a bath of insulated water at an initial temp of say 25 deg C, let the hand warmer work in the water, then measure the temperature of the water later after the hand warmer runs out. Then take the temperature difference of the water, the amount of water and using the equation:

q = mct

q - amount of energy
m - mass of water used in water bath
c - specific heat capacity of water
t - different in temperature

Get q, that is your answer.

Note: better to use more water, not too much or the change in temperature will be too hard to detect, and not too little, as we do not want to have to factor in the heat capacities of the equipment we used (thermometer, bucket...) as it will make calculations complicated.

Answer 2

Are you talking about an actual experiment or the chemical reaction with the energy released shown?
For an experiment do a simple calorimetry experiment. Place the hand warmer in a know amount of water (in a calorimeter{a stryrofaon cup will work}). Measure the rise in temperature of the water. Use the energy equation to find the energy released.
Energy = (mass of water) x change in temperature x Specific heat of water( in either calories or joules per gram)

Answer 3

Hi. You mean those things you fill up with naptha?

If you give the amount of ml you used to chage it with I'll tell you how much fuel value the naptha had.