Which of the following would cause a physical change in a bar of steel?
a.) combining it with other substances to form new substances
b.) hammering it into a new shape
c.) putting it in water to form rust
d.) putting it in a box

the equation that correctly represent the reaction for formation of ammonia is

n2+ 3h2 → 2nh3 (answer d)

1 mole of nitrogen gas (n2) react with 3 moles of hydrogen gas (h2) to form 2 moles of ammonia ( nh3). this is in a process known as haber process were iron is used as a catalyst and reaction take place that a higher temperature and pressure. the process is exothermic hence energy is released.