Question 18

[eo]

I feel like # 18 answer choices are missing something.... Howd do you kow that I2 must be heated to form a gas?

[admin]

From general chem to bio!

When you think of hydrogen, you think of a gas (hydrogen's most thermodynamically stable state). When you think of mercury (Hg), you think of a liquid.

Well, what form do you think of iodine? Most will recognize it is a liquid (present in the brown liquid used to sterilize wounds) or present as a solid (in a mineral or salt; you will see many companies specifically state on a bag or box of salt that iodine is present; this was started to reduce the incidence of goiters, a disease of the thyroid which needs iodine for hormones like thyroxine). Whether you thought of it as a liquid or solid, clearly energy would be required to have it become a gas.

There was a subscript issue with Hg.

[Matthew]

Dr. Ferdinand,

PS-7 has been a tough challenge. I read in my mcat book that all elemental forms or whether reactant or products are zero by rule. Example O2, H2. I put answer A, but answer says C. Why can't A be the answer.

[admin]

Yes, this test is a challenge.

The information that you stated is correct. Unfortunately, whether or not A is a good answer choice depends on what time you took your practice test! The day before you posted, answer choice A had a typo which was corrected to read: H(g) which is not the elemental form of hydrogen (as you correctly stated, H2(g) is).