Let's look at the different types of conditional sentences to figure out what each sentence means.
Note: There are two clauses in a conditional sentence: the "if" clause and the main clause. The main clause is the independent clause, whereas the "if" clause is dependent.
If you don't want to read the whole answer, scroll to the bottom to find the "main points."
Type 0
This is used when the situation is real/possible and the main clause is always true when the "if" clause is true. This is used for general truths.
Example:
If you die, your heart stops.
The "if" clause uses the simple present tense, and the main clause also uses the simple present tense.
A trick to use to check if a sentence is of type 0 is to see if "if" and "when" can be used interchangeably; if they can be, then it is of type 0.
Type 1
This is the type of conditional that your second sentence is.
This is used when the situation is possible and the mains cause is probable when the "if" clause is true. The sentence refers to the present or future.
Example:
If you use profane language, the teacher will reprimand you.
The "if" clause uses the simple present tense, and the main clause uses the simple future tense.
Type 1 is distinct from type 0 because the result (main clause) of type 1 conditionals is probable, but not guaranteed. In the above example for type 1 conditional, it is possible the teacher is out of earshot, so there is no guarantee that you will be reprimanded (or the teacher could simply be indifferent to the use of profane language).
Type 2
This is the type of conditional that your first sentence is.
This is used when the situation is unrealistic and the main clause is probable when the "if" clause is true. The sentence refers to any time.
Examples:
If I was confident, I wouldn't care about how I look.
and
If I was confident, I would be wearing that bikini.
The "if" clause uses the simple past tense, and the main clause uses the simple present conditional or the progressive present conditional tense. The simple/progressive present tenses are made conditional by adding a modal auxiliary verb (such as "would") to the main verb.
Type 3
This is used when the situation is hypothetical and in the past; the main clause was probable, but did not actually happen.
Example:
If I had fallen, I could have broken my arm.
and
If I had fallen, I would have been airborne for a few seconds.
The "if" clause uses the past perfect tense, and the main clause uses the perfect conditional or progressive perfect conditional tense. The perfect/progressive perfect tenses are made conditional by adding a modal auxiliary verb (such as "would") to the main verb.
Now we can understand the subtle differences in their meanings.
The first sentence, which falls under the category of type 2, implies that you will probably never be asked to describe yourself.
The second sentence, which is type 1, insinuates that you will likely be asked this question in the future.