5. Which of the following statement is correct? a. Grinding solid solutes decreases their solubility. b. Grinding solid solutes speeds up their solubility. c. Stirring slows down the solubility of solute in a solvent. d. Heating slows down the solubility of solute in a solvent.
Answers
Answer:
Solubility
Temperature
Effect of temperature on liquid and solid solutes
As temperature increases, the solubility of a solid or liquid can fluctuate depending on whether the dissolution reaction is exothermic or endothermic.
Increasing solubility with increasing temperature
In endothermic dissolution reactions, the net energy from breaking and forming bonds results in heat energy being absorbed into the system as the solute dissolves. When the temperature of the system increases, additional head energy is introduced into the system.
So according to Le Chatelier’s Principle, the system will adjust to this increase in the heat by promoting the dissolution reaction to absorb the added heat energy. Increasing the temperature will therefore increase the solubility of the solute.
An example of a solute whose solubility increases with greater temperature is ammonium nitrate, which can be used in first-aid cold packs. Ammonium nitrate dissolving in solution is an endothermic reaction. As the ammonium nitrate dissolves, heat energy is absorbed from the environment causing the surrounding environment to feel cold.
Decreasing solubility with increasing temperature
In exothermic reactions, heat energy is released when the solute dissolves in a solution. Increasing temperature introduces more heat into the system. Following Le Chatelier’s Principle, the system will adjust to this excess heat energy by inhibiting the dissolution reaction. Increasing temperature, therefore, decreases the solubility of the solute.
An example of a solute that decreases in solubility with increasing temperature is calcium hydroxide, which can be used to treat chemical burns and as an antacid.
Effect of temperature on gas solutes
In general, heat energy is released as gas dissolves in solution, meaning the dissolution reaction is exothermic. As such, a gas becomes less soluble as temperate increases.
Increasing temperature results in increased kinetic energy. Gas molecules with greater kinetic energy move more rapidly resulting in the intermolecular bonds between the gas solute and solvent breaking.
Pressure: Henry’s law
The solubility of gas is affected by changes in pressure on the system. A gas dissolves in liquids to form solutions. This results in equilibrium in the system where a proportion of gas molecules is dissolved in liquid while the rest remains in gaseous phase above the liquid.
Henry’s law states that: “At constant temperature, the amount of gas that dissolves in a volume of liquid is proportional to the partial pressure of the gas in equilibrium with the liquid.”
Henry's law results in the following equation: C = kP
Where:
C represents the solubility of the gas at a certain temperature in a specific solvent
K represents Henry’s law constant
P represents the partial pressure of the gas i.e. the pressure the gas exerts on the system at a given volume and temperature
Hence as the pressure of the gas above the liquid in the system increases, the gas molecules become more soluble in the solvent. Likewise, if the pressure of the gas in the system decreases, gas becomes less soluble in the solvent.