Step 3: Determine the amount of energy change in the reaction. a) Use the table of enthalpy values (Table A) provided in the Student Worksheet to locate the enthalpy of formation (∆Hf) for each reactant and each product. Record these values along with the reactants and products in Table B of the Student Worksheet. b) Determine the total enthalpy of the reactants and the total enthalpy of the products. Record these values in Table C of the Student Worksheet. c) Use the following formula to find the net change in enthalpy for the reaction and to determine whether the reaction is endothermic or exothermic.

Explanation:

Assume the reaction is the combustion of propane.

Word equation: propane plus oxygen produces carbon dioxide and water

Chemical eqn:    C₃H₈(g) +   O₂(g) ⟶   CO₂(g) +   H₂O(g)

Balanced eqn:    C₃H₈(g) + 5O₂(g) ⟶ 3CO₂(g) + 4H₂O(g)

(a) Table of enthalpies of formation of reactants and products

(b)Total enthalpies of reactants and products

ΔᵣH° is negative, so the reaction is exothermic.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.