Because of the violence of the French Revolution, no one was concerned with attending concerts.
Because composers were writing nationalistic music, they did not write music depicting anything outside of their homeland, lest they be labeled a traitor.
The incorporation of extra-musical elements into music became common and was known as "program music."
The symphonic poem was invented by Vivaldi, but developed in the romantic era by Franz Liszt.
Brass instruments were given valves.
Harps were given double-action.
Pianos were given pedals.
String instruments were given tuning pegs.
Highly expressive and emotional
Use of rubato
Wide range of dynamics
Here's an interesting quiz for you.