Chem 1220: Lecture 3 Flashcards
What happens to entropy during mixing?
Entropy almost always increases during mixing, which encourages the mixing process
Why are ΔHsolute and ΔHsolvent always positive?
Because intermolecular forces are being broken
Why is ΔHmix always negative?
Because new intermolecular forces are being formed
What indicates if a mixing process is endothermic or exothermic?
When ΔHsoln is positive, the mixing process is endothermic and the flask will feel cold
What are the different ways to express solution concentration?
- Mass Percentage
- Parts per million (ppm)
- Parts per billion (ppb)
- Mole Fraction
- Molarity (M)
- Molality (m)
What is the formula for molarity (M)?
Molarity (M) = moles of solute / liters of solution
What is the formula for Molality (m)?
Molality (m) = moles of solute / kilograms of solvent
What is the key difference between Molarity and Molality?
Molarity uses liters of solution in denominator, while Molality uses kilograms of solvent in denominator
How does temperature affect gas solubility?
Gas solubility decreases as temperature increases
Which will be more soluble in water: Hexane (C₆H₁₄), Hexanol (C₆H₁₄O), or 1,6-Hexanediol (C₆H₁₄O₂)?
1,6-Hexanediol will be most soluble because it has two OH groups, making it the most polar of the three compounds
What happens when a solution becomes supersaturated?
It contains more dissolved solute than is normally possible under given temperature conditions
How do you convert a mass percentage to moles?
First find the mass of solute (multiply total solution mass by percentage), then divide by molar mass of solute
For most solid solutes, how does temperature affect solubility?
Solubility typically increases as temperature increases
What units are typically used for expressing very dilute solutions?
Parts per million (ppm) or parts per billion (ppb)
What is the relationship between pressure and gas solubility?
Gas solubility increases as the partial pressure of the gas above the solution increases (Henry’s Law)
