What's the difference between "spontaneous" and "impulsive"?

What's the difference between "spontaneous" and "impulsive"?

When a person is "spontaneous," it usually has a positive meaning.

Examples:

1. The people at the concert were so excited by the singer's performance that they spontaneously stood up and sang with her.

2. John's wife is so spontaneous: she hums whenever the moment feels right to her.

When a person is "impulsive," it usually has a negative meaning.

Examples:

1. Sandi is so impulsive: she buys whatever she likes in a store, whether she needs it or not.

2. Bill was feeling lucky, so he impulsively drove to Las Vegas to try to win some money.