# 7.7.1: Practice Stoichiometry Part 3

Exercise $$\PageIndex{1}$$

2 NO (g) + O2 (g) $$\rightarrow$$ 2 NO2 (g)  $$\Delta H$$=  – 114 kJ

Is the reaction above endothermic or exothermic? What is the energy change when 0.633 moles of NO react?

Exothermic. Energy change is – 36.1 kJ, meaning that 36.1 kJ of energy is released.

Exercise $$\PageIndex{1}$$

CaCO3 (s) $$\rightarrow$$ CO2 (g) + CaO (s) $$\Delta H$$=  + 192 kJ

Is the reaction above endothermic or exothermic? What is the energy change when 2.87 grams of CaCO3 react?

Endothermic. Energy change is + 5.51 kJ, meaning that 5.51 kJ of energy is absorbed.

Exercise $$\PageIndex{1}$$

S8 (s) + 12 O2 (g) $$\rightarrow$$ 8 SO3 (g)  $$\Delta H$$=  – 3166 kJ

Is the reaction above endothermic or exothermic? What is the energy change when 26.7 grams of SO3 are produced?

Exothermic. Energy change is – 132 kJ, meaning that 132 kJ of energy is released.

Exercise $$\PageIndex{1}$$

2 HCl (g) $$\rightarrow$$ H2 (g) + Cl2 (g) $$\Delta H$$=  + 185 kJ

Is the reaction above endothermic or exothermic? What is the energy change when 489 grams of HCl react?