Is Ammonium Chloride (NH4CL) an endothermic reaction when in water?

Question

I was wondering if Ammonium Chloride is an endothermic reaction when mixed with water in a calorimeter and what the effect of increasing the amount of water in the calorimeter would have on the reaction. I have hypothesised that the temperature of the chemical reaction between water and Ammonium Chloride will heat up at a faster rate in 10ml of water compared to 50ml and to 100ml. In correspondence to the second law of thermodynamics and the kinetic molecular theory, there are a greater number of molecules in 100ml of water compared to 10ml of water, resulting in more molecules needing to be heated.

However, I'm not sure if this is correct.

In my experiment, the temperature of 3g of Ammonium Chloride-in 10ml, 50ml, 100ml- over the first two minutes instantly drops, however, it increases in temperature again in the next 3 minutes. Why would that be?

Answer 1

You have asked several questions and I will try to answer them in order.

Yes, the dissolution of ammonium chloride in water is endothermic.

The effect of the volume of water would be that the greater the volume of water, the smaller the change in temperature. So, for example, the change in temperature in 10 mls would be about 10x the change in temperature in 100 mls of water. The rate of change would not be significantly different. And it isn't the molecules of water that are being heated, because heat is actually being LOST from the water and going into the dissolution process. This is why it's an ENDOTHERMIC reaction.

In your experiments, the temperature will instantly drop (in your case over about 2 minutes) because the water is losing heat to the dissolution process. After that the temperature will increase until it comes into equilibrium with the room temperature.

Hopefully, this answers your questions.