Emergent gameplay is when the game can be solved using methods unforeseen by the programmers, whether by design (giving the player tools and physics to create their own solution) or by accident (glitches, bugs, unforeseen AI behaviour)
Now, in Scribblenauts, I rescued the kitten by using two laser swords and a piece of glue. I doubt the programmers intended laser sword polevaulting as a possible solution, but it works. A non-emergent solution would be summoning a fireman. Firemen rescue kittens, and this is also a solution to the puzzle.
Scribblenauts has emergent gameplay because it gives you enough tools to think of your own solutions and allows for solutions the programmers could never have thought of themselves.
The objects you can summon are mostly prettier copies of similar objects, but that's because they wanted you to be really able to summon almost anything. If they stuck to just one of each functional object, you'd have a menu with objects to pick from.
It's called "Scribblenauts", and the main character wears a chicken hat. I don't think anyone ever meant for the game to have complex chemistry.
Sandbox games always get boring soon anyways. The best sandbox there is is the real world, but still people go play computer games because they're bored, then complain because the sandbox game they're playing gets boring.
Physics are boring, you already know the rules of physics. Once you've messed around a bit you already know what will happen even though you've never done it before. People are great at recognizing patterns. If you really want to captivate an audience, provide a storyline, a preset goal, a human opponent, whatever. Just sandboxing itself is a recipe for dullness no matter how detailed.