Coal tar pitch is a complex carbonaceous substance, and its chemical and physical properties will change at high temperature. When coal tar pitch is heated to 500 degrees, the following changes will occur:

1. Loss of volatile substances: Volatile components in coal tar pitch began to escape, making it more dense and stable.

2. Formation of reactive substances: Due to the fracture and recombination of coal tar pitch molecules at high temperature, its molecular structure has changed and some reactive substances, such as benzene and benzene derivatives, have been formed.

3. Increase chemical reactivity: At high temperature, the chemical reactivity of coal tar pitch is enhanced, and it is easy to react with oxygen and other gases to burn.

4. Coke formation: When the coal tar pitch is heated above 500 degrees, the carbon elements in it begin to gather to form coke.

Generally speaking, coal tar pitch will become denser, more stable and more reactive when heated to 500 degrees, and will produce a lot of coke.