This says, place 50ml of water in a calorimeter. Weigh about 2g of NaOH pellets

Question

This says, place 50ml of water in a calorimeter. Weigh about 2g of NaOH pellets and add them to the water to dissolve. Record the highest temperature reached. It asks to state what the surroundings are, choosing all that apply:

Water
The air all around in the lab
NaOH Pellets
Styrofoam cup calorimeter

I selected, air in the lab alone first, then both air in the lab and styrofoam calorimeter, and finally air, pellets and styrofoam calorimeter. They all came up wrong. Really confused as what are the surroundings supposed to be here?

Update: Well surroundings to be precise. Both System and surroundings

Explanation / Answer

NaOH pellets when put in water following chemical reaction will happen.

NaOH(s) + H2O(l) => Na+ + OH- + H20 + HEAT

It is a highly exothermic reaction.So huge amount of heat will be released.The temperature of the solution increases considerably.

The temperature of the surroundings will also increased.

Since the reaction taking place in the calorimeter is open to the atmosphere, the enthalpy change is measured directly by the device. The insulation provided by the styrofoam ensures that any heat absorbed or released by the system (reactants and products) goes only to the solvent . the surroundings are restricted to the solvent . The thermometer gives temperature of the surroundings to be measured. By the First Law of Thermodynamics , we know any heat lost by the system must be absorbed by the surroundings, or:

-qsystem = qsurroundings

which can be measured, and the heat capacity of the solvent in the caloriemeter, the heat lost by the system can be calculated. Since the pressure is constant, this is equal to the enthalpy change for the process.

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