Examine the unbalanced equation. + → which of the answer choices shows the balanced equation? a. 4al + 3o2 → 2al2o3 b. 2al + 3o2 → 4al2o3 c. 2al + 2o2 → 2al2o3 d. 4al + 2o2 → 4al2o3

Which of the following statements is true? a. most heat energy is easily recovered and used for useful actions. b. friction causes molecules to vibrate more slowly. burning air and gasoline in an c. engine changes chemical energy into mechanical energy. it is impossible to d. change mechanical energy into mechanical energy.