Auto Parts: catalytic converter..., toyota corolla 1999, toyota corolla

Question
hello, i owned a toyota corolla 1999 and i was wondering what an catalytic converter actually does. i took my car to my mechanic because the car starting making noises every time i accelerated, and it turned out to be that it was my muffler. the mechanic said that i needed to get a new converter. what are the effects it has on the car and are they expensive?
  thank you for your time.

Answer
they are usually a couple of hundred dollars for the correct one. it causes a chemical reaction with unburnt fuel traveling through it which in turn completely burns the fuel. nowadays a car will run better with one on than off due to technology advances. if and when they get clogged they will cause a restriction of flow and they might also break internally which can also restrict flow hurting performance and mileage.