Once you have finished ch. 7 and become somewhat familiar with enthalpy, I want

Question

Once you have finished ch. 7 and become somewhat familiar with enthalpy, I want you to look at a culinary process which exploits the system and surroundings around an endothermic process- making ice cream! You can make ice cream using an ice cream maker or even using dry ice, if you like. If you have a source you can even make your own ice cream with liquid nitrogen! However, if you prefer to buy it you can go to a local shop which makes ice cream in front of you using liquid nitrogen, like a Sub Zero location (they have spots in Murray, Sandy, and Jordan Landing among others). (Sub Zero does have dairy free options). Once you have eaten it, I want you to come back here and report about your experience. Include the following details: 1 - What kind of ice cream did you make or get? 2 - What process was used to make it? 3 -Describe the thermodynamic changes that occurred in the process. What was endothermic and what was exothermic? How would you define the 'system and the surroundings' for this process? 4 How are thermodynamics involved in making the ice cream 'creamy' vs. grainy' (like what you get with freezer burned ice cream)? 5- What did you think of the overall experience? Enjoy!!

Explanation / Answer

As it is given that we are free to choose any above given methods, let us choose Ice-cream using DRY ICE.

First i would like to give a short insight of Ice-cream making using dry ice.

Dry ice is generally Carbondioxide(CO2) in solid form with a temperature of -78.5C. Firstly, we crush this dry ice into tiny pieces and mix them with cream (used for making ice-cream). Then, we will mix thoroughly so that the cream continuously gives its heat to the dry-ice which is at a lower temperature than the cream (heat flow from hotter to colder body an obvious phenomenon) and slowly the cream changes into a solid Ice-cream.

Actually a lot more process is involved in making Ice cream but as thermodynamics part is considered, the above insight is quite sufficient.

Now, lets look at some thermodynamics and heat transfering processes.

Generally, dry ice dont have a liquid phase. So it directly transfers heat (to room in which we are making ice-cream) changing its state from solid to gas. So it instantly takes the small changes in temperatures beside it. Lets us look at some questions araising. Why do we add dry ice to ice-cream?? What is the process involved??

Our aim is to make the cream in liquid form to a solid(more if a semi-solid) form. How can we make this happen?? Simple, just by taking the heat out of system. How can we take heat out of system?? Again, just by keeping a colder body beside the cream. So. we add dry-ice (which is colder than cream) to cream and this allows cream to transfer its heat to dry-ice and change its form to solid.  

The process here is Exothermic with respect to cream (as cream gives out the heat to surroundings) and Endothermic with respect to dry-ice (as dry-ice takes the heat from surroundings).

Coming to the questions part, we can answer them easily based on the explaination given above.

I'II give basic answers to the questions and you can even modify them based on the theory explained.

ANSWERS:

1. Dry-ice

2. Exothermic process (as we are concerned only with cream which is our system).

3. Exothermic is cream changing to solid Ice-cream, and Endothermic is Dry-ice taking heat given by cream. Our SYSTEM is CREAM and SURROUNDING is DRY-ICE.

4. Its actually involves a deep insight, but generally water present in cream is broken down into tiny particles by mixer. So, smaller the particles of water (as temperature of cream drops water changes from liquid to solid) smoother the Ice-cream and bigger the particles of water, granier it is.

5. We had a good insight into Heat and thermodynamics of bodies and clearly seen the changes in phase of water (or any substance) and we are able to relate this to heat transfer logics.

NOTE : Based on your understanding, 5th answer can be changed accordingly.

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