Which of the following best describes H2(g) + Cl2(g) 2HCl(g), H = -184.6 kJ/mol? close
A.
The reaction is endothermic.
B.
The reaction requires heat.
C.
The reaction produces heat.
D.
The reaction has no activation energy.
The answer is C. The reaction produces heat.

They carry out the exchange of gases as we breathe ( oxygen and carbon dioxide).

Maybe you should get some from your teacher and learn more so you can get your grades up and maybe study a bit more

Qrepresents joules in the formula

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.