Question

When a mole of lithium reacts chemically with hydrogen to form lithium hydride, the energy released is found to be roughly 90 joules. How much mass is lost?
Answer

1.0 x 10-15 kg

2.7 x 1010 kg

1.0 x 1015 kg

3.0 x 10-7 kg

Answer 1

they want you to use \(\sf E=mc^2\)

Answer 2

E=mc^2 --> m= E/c^2 = 90 J / (3*10^8)^2 =1.0x10^-15 kg