Calculate the theoretical flame temperature when ethylene at 25°C is burned with: (a) The theoretical amount of air at 25°C. (b) 25% excess air at 25°C. (c) 50% excess air at 25°C. (d) 100% excess air at 25°C. (e) 50% excess air preheated to 500°C. (f) The theoretical amount of pure oxygen. 4.22. What is the standard heat of combustion of each of the following gases at 25°C if the combustion products