University:
Campbell University
Course:
CHEM 111 | General Chemistry I
Academic year:

2024
Views:

431

Pages:

2
Author:

todaviaaquik4l

KEY Energy Changes in Chemical Reactions Name - _______________ 1.) You can think of this reaction, CH4 + 2 O2 CO2 + 2 H2O , as occurring in two steps (it doesn’t  go this way, but it is convenient to think of it this way). Step 1 - CH4 + 2 O2 Step 2 - C + 4H + 4O  C + 4H + 4O  (the reactants are broken down to individual atoms) CO2 + 2 H2O (the individual atoms are assembled into products) a.) Does step 1 absorb or give off energy? absorb b.) Does step 2 absorb or give off energy? give off c.) Since the overall reaction is exothermic, which step involves more energy, step 1 or 2? Step 2 2.) The energy needed to break an H-Cl bond is 432 ݇‫ܬ‬. 2 HCl + 432 ݇‫ܬ‬  H2 + Cl2 How many kilojoules of energy are given off in the following reaction? Why? H2 + Cl2  HCl + _432_ kJ Answer – The two reactions are the exact opposite of each other. 3.) Is the burning of wood exothermic or endothermic? Answer – exothermic as heat (energy) is produced. 4.) Is the melting of sugar exothermic or endothermic? Answer – endothermic as heat (energy) is absorbed by the sugar to change phases. 5.) A beaker becomes warm when a reaction occurs in it. Are the chemicals in the beaker gaining or losing energy? Is the reaction endothermic or exothermic? Answer – losing energy. Exothermic as energy is released (lost). 6.) Which contains more energy in an endothermic reaction, the reactants or products? Answer – products. The reactants gain energy to become high energy products. 1 KEY 7.) In an exothermic reaction, do you have to add or remove energy in order to allow particles to form? Answer – remove energy from reactants as lower erngy products are formed. 8a.) Is ∆‫ > ܪ‬0 or ∆‫ < ܪ‬0 for an endothermic reaction? b.) Is ∆‫ > ܪ‬0 or ∆‫ < ܪ‬0 for an exothermic reaction? Hreactants ‹ Hproducts and ∆H = Hp - Hr ∆‫ < ܪ‬0 9.) Draw an energy diagram having ∆‫ = ܪ‬+25 ݇‫ܬ‬. Energy (kJ) Products ∆‫ = ܪ‬+25 ݇‫ܬ‬ Reactants Reaction Proceeds  10.) Draw and energy diagram having ∆‫ = ܪ‬−50 ݇‫ܬ‬. Energy (kJ) Reactants ∆‫ = ܪ‬−50 ݇‫ܬ‬ Products Reaction Proceeds  11.) ∆‫ = ܪ‬−50 ݇‫ ܬ‬for the reaction F  G. Re-write this equation to show the 50 ݇‫ ܬ‬properly on the reactant or product side. Answer – F  G + 50 ݇‫ܬ‬ 12.) If a reaction absorbs 30 ݇‫ ܬ‬of heat, what is the ∆H for the reaction? ∆‫ = ܪ‬+30 ݇‫ܬ‬ 13.) If P  Q + 25 ݇‫ܬ‬, what is the ∆H for the reaction? Which have more energy, the reactants or products? ∆‫ = ܪ‬−25 ݇‫ܬ‬ reactants have more energy. 2