Final answer:
The main difference between anti-ice and de-ice is that de-icing removes ice after it has formed, while anti-icing is a preventative measure. On roadways, salts like sodium chloride or calcium chloride are used for de-icing, but for aircraft, covalent compounds such as ethylene or propylene glycol are preferred to prevent ice from forming and avoid corrosion.
Step-by-step explanation:
The difference between anti-ice and de-ice lies in the timing and purpose of each process. De-icing involves removing ice that has already formed, whereas anti-icing is the process of preventing ice from forming in the first place. For de-icing, salts such as sodium chloride or calcium chloride are commonly used on roadways because they lower the freezing point of water, which helps to melt the existing ice. These salts are effective because they break down into ions which depress the freezing point. However, since these ionic compounds accelerate metal corrosion, they are not suitable for use on airplanes. Instead, for the anti-icing of aircraft, covalent compounds like ethylene or propylene glycol are used. These substances not only lower the freezing point but also raise the boiling point of the liquid, making it useful in winter as a de-icing agent and in summer as an antifreeze solution.