What is the difference between these two Japanese sentences? Kono uchi ni hon ga arimasu ka and Kono uchi ni hon desu ka
The difference between these two is that the first sentence is grammatically correct while the second sentence is not. The second sentence does not have an actual meaning because of the incorrect use of "desu."
The problem here is that "desu" does not work exactly like "is" in English. If it did, the second sentence would mean "is there a book at this house," which is what the first sentence means. But "desu" does not work that way. "Desu" is used like a "to be" verb, but only in sentences that describe something or someone. You can say "watashi wa gakusei desu," meaning "I am a student" because "student" describes what you are. You can say "kyou wa atsui desu," meaning "today is hot" because "hot" describes today. But you cannot say "kono uchi ni hon desu" to mean "there is a book at this house" because "book" does not describe "house."
So, when using "desu" you have to be making a sentence that describes something. Because you have used "desu" in an incorrect way, the second sentence has no real meaning in proper Japanese.