ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: kenhung123 on November 09, 2010, 05:33:42 pm

Title: surface area
Post by: kenhung123 on November 09, 2010, 05:33:42 pm: Lisachem reckons a solid would decrease in SA with time of a reaction, but it increases right? If the solid gets smaller there is more SA:V ratio?
Title: Re: surface area
Post by: ghadz7 on November 09, 2010, 05:36:46 pm: No I think the solid would be consumed in the reaction. The ratio only works for the same amount of solid when comparing powdered substance to lumps.
Title: Re: surface area
Post by: /0 on November 09, 2010, 05:44:29 pm: You could try thinking about it in terms of a spherical solid (usually a good approximation)

The surface area is $4\pi R^2$ , which decreases as R decreases.

But SA:V ratio is $\frac{4\pi R^2}{\frac{4}{3}\pi R^3}=\frac{3}{R}$ , which increases as R decreases.
Title: Re: surface area
Post by: Mao on November 09, 2010, 06:01:29 pm: Quote from: kenhung123 on November 09, 2010, 05:33:42 pm
Lisachem reckons a solid would decrease in SA with time of a reaction, but it increases right? If the solid gets smaller there is more SA:V ratio?

Yes. The SA:V ratio increases, but SA itself decreases.
Title: Re: surface area
Post by: kenhung123 on November 09, 2010, 06:11:30 pm: Ah I get it. I got confused with questions that concern whether a large solid or small solid should be used to increase reaction rate...Thanks guys