Question

The thermite reaction demonstrated in class requires high temperatures to start the reaction. A simple open flame is not enough to start the reaction. Once the reaction is going, then it generates enough heat to keep the reaction going. According to the literature on thermite, it takes temperatures of about 2200 C to start the reaction. If you need to heat up one gram of thermite (assumed to be 25% aluminum metal and 75% iron oxide) to start the reaction, then how many joules of heat must the ignition system provide? Assume the heat capacity of aluminum is 0.90 J/g-K and iron oxide is 0.45 J/g-K and that your thermite mixture starts at room temperature of 20 C. Ignore any enthalpy of phase changes that may occur in heating up the mixture.

Answer 1

1 g thermite--25% Al; 75% Fe2O3 makes
0.25g Al and 0.75g Fe2O3.

q = [mass Al x specific heat Al x (Tfinal-Tinitial)] + [mass Fe2O3 x specific heat Fe2O3 x (Tfinal-Tinitial)]
Substitute and solve for q.

Answer 2

56