Is the total enthalpy (H) of the reactants for an endothermic reaction greater than or less than the total enthalpy of the products?

Classify each of the following as exothermic or endothermic:

a. CH₄(g) + 2O₂(g) $\xrightarrow{∆}$ CO₂(g) + 2H₂O(g) + 802kJ

The equation for the formation of silicon tetrachloride from silicon and chlorine is

Si(s) + 2Cl₂(g) → SiCl₄(g) + 157 kcal

b. Is the energy of the product higher or lower than the energy of the reactants?

The equation for the formation of silicon tetrachloride from silicon and chlorine is Si(s) + 2Cl₂(g) → SiCl₄(g) + 657 kJ

b. Is the energy of the product higher or lower than the energy of the reactants?

In photosynthesis, green plants convert carbon dioxide and water into glucose (C₆H₁₂O₆) according to the following equation:

6 CO₂(g) + 6 H₂O(l) → C₆H₁₂O₆(aq) + 6 O₂(g)

b. Is the reaction endothermic or exothermic?

The vaporization of Br₂ from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol).

a. What is the sign of ∆H for this process? Write a reaction showing heat as a product or reactant.

Oxygen can be converted into ozone by the action of lightning or electric sparks:

3 O₂(g) ⇌ 2 O₃(g)

For this reaction, ∆H = +69kcal/mol (+285 kj/mol) and K = 2.68 × 10^-29 at 25 °C.

a. Is the reaction exothermic or endothermic?

Hydrogen chloride can be made from the reaction of chlorine and hydrogen:

Cl₂(g) + H₂(g) → 2 HCl(g)

For this reaction, K = 26 × 10³³ and ∆H = -44 kcal/mol(-184 kJ/mol) at 25 °C.

a. Is the reaction endothermic or exothermic?

What is measured by the heat of reaction?