Lecture 12 - Solutions and Mineral Reactivity

Question 1

When dHsolv is endothermic which way will the reaction proceed when temperature is increased?

Answer 1

It will be driven to the product side as there will be increased solubility
When dHsolv is exothermic an increase in temperature will drive it to the reactant side as solubility will decrease

Question 2

What are the hydration effects on the thermodynamic state of solution?

Answer 2

Enthalpic = less energy needed to break bonds
Entropic = more configurations of water molecules possible. Less time in hydration shell

Question 3

How can system undergo a dissolution reprecipitation mechanism?

Answer 3

• Depends on what the system is in equilibrium with
• If in eq. with ACC, it will be supersaturated with vaterite
• When in vaterite stage, less carbonate needs to be in eq. with calcite than ACC
• Thus, reprecipitation can occur

Question 4

what shape do you predict for a diffusion controlled reaction?

Answer 4

Diffusion is slow but there is rapid addition of parts. Thus it will grow quickly and outwards to form a dendrite shape. e.g. snowflakes

Question 5

what shape do you predict for an interface controlled reaction?

Answer 5

This means diffusion is fast but slow addition of parts. This gives the system time to become more structured, and so a euhedral structure is formed