Question

Solid potassium hydroxide may be used to unclog sink drains. the dissolution of potassium hydroxide in water is quite exothermic. what are the signs of δhsys and qsurr?

Answer 1

Answer: The sign of
`\Delta H_(sys)` will be negative (-) and that of
`q_(surr)` will be positive (+).

Explanation: We are given a reaction of potassium hydroxide and water which is exothermic in nature.

Exothermic reactions are the reactions in which there is release of heat energy.

• For
  `\Delta H`

In these reactions, the energy of the products is lower than the energy of the reactants.

`\Delta H=H_(products)-H_(reactants)`

Hence, energy change for the system will be negative (-ve).

• For 'q'

'q' is the heat.

According to the convention,

q = +ve ; when heat is absorbed.

q = -ve ; when heat is released.

As the heat is transferring from system to surrounding, so the heat is absorbed by the surrounding. Hence, the sign of 'q' will be positive (+ve)

Answer 2

Answer is: The sign of ΔHsys is - and the sign of qsurr is +.

First Law of Thermodynamics - any heat lost by the system must be absorbed by the surroundings.

-qsystem = qsurroundings.

There are two types of reaction:

1) exothermic reaction (chemical reaction that releases more energy than it absorbs).

For example, ΔH(reaction) = -225 kJ/mol; this is exothermic reaction.

2) endothermic reaction (chemical reaction that absorbs more energy than it releases).