You are going to a chemical cold pack using NHNOs and water. You have 100 mL of

Question

You are going to a chemical cold pack using NHNOs and water. You have 100 mL of water that is at 25.00 °C. You want the temperature of the water to decrease to 5.00 ·The heat absorbed by NH4NO3 when it dissolves is 25.41 kJ/mole. Determine how many grams of NH NOs you need to make the cold pack. The parts below might help you think about how to solve the problem. 2. a. What other information might you need? How many joules of energy need to be absorbed to decrease the temperature of the water to 5.00 °C? b. c. How much NH,NO, is required to drop the temperature that amount?

Explanation / Answer

Assuming no heat loss to the surroundings:

Heat lost by water = Heat absorbed by NH4NO3

Heat lost by water = m*C*dT

Here, C is specific heat capacity of water = 4.184 J/(g.0C)

Putting values:

Heat lost by water = 100*4.184*(25-5) = 8368 J

Here we have assumed that density of water is 1g/mL.

MW of NH4NO3 = 80.04 g

So,

80.04 g of NH4NO3 dissolves by absorbing 25410 J of heat.

So, amount of NH4NO3 that can be dissolved by absorbing 8368 J of heat = (80.04/25410)*8368 = 26.36 g

Hope this helps !

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