1. 1.2.1 Enthalpy

2.  Enthalpy is the heat content of a system, or the amount of energy within a substance, both kinetic and potential.  Every substance possesses both potential energy, and kinetic energy from to the constant motion of the particles. This total amount of energy is enthalpy.

3.  Symbol for enthalpy: H  Unit for enthalpy: the joule, J

4.  It isn’t possible to directly measure the heat content of a substance- chemists can only measure how much enthalpy changes  Therefore, we will generally refer to the change in enthalpy, or Δ H. This is also know as the heat of the reaction.

5.  During exothermic reactions, more energy is released during bond formation than is required to break bonds. An exothermic reaction is written like this:  Cu(s) + Cl 2 (g) → CuCl 2 (g) + 220.1 kJ  There is a net release of 220.1 kJ of energy, this appears on the product side.

6.  Exothermic reactions release energy because the reactants have more potential energy than the products.  The "excess" energy is released to the surroundings.

7.  This can be shown graphically.  The graph illustrates the amount of potential energy of the products is less than that of the reactants; potential energy decreased.

8.  When the amount of entropy in a system decreases a negative sign to indicate the drop.  Thus, we could rewrite the equation shown above as:  Cu(s) + Cl 2 (g) → CuCl 2 (g) + 220.1 kJ  Cu(s) + Cl 2 (g) → CuCl 2 (g) Δ H° = -220.1 kJ

9.  During endothermic reactions, energy is absorbed from the surroundings. An endothermic reaction is written with the energy term on the reactant side:  H 2 O(g) + C(s) + 132 kJ → CO 2 (g) + 2H 2 (g)  H 2 O(g) + C(s) → CO 2 (g) + 2H 2 (g) Δ H° =132 kJ

10.  An input of energy is required  The potential energy of the reactants is lower than the potential energy of the products; energy must be added to the reaction for it to occur.

12.  We can remove the energy term from the equation and write it as a positive value, indicating that enthalpy increased:  H 2 O(g) + C(s) → CO 2 (g) + 2H 2 (g) Δ H° = +132 kJ

13. 1.Identify each of the following reactions as exothermic or endothermic.  CH 4 (s) + 2O 2 (g) → CO 2 (g) + 2H 2 O(l) Δ H° = -890 kJ  2HCl(g) → H 2 (g) + Cl 2 (g) Δ H° = 185 kJ  4NH 3 (g) + 5O 2 (g) → 4NO(g) + 6H 2 O(l) Δ H° = -1169 kJ 2.When potassium nitrate dissolves in water, the beaker containing the solution gets cooler. Is dissolving this salt an exothermic or an endothermic process?

14.  1.Identify each of the following reactions as exothermic or endothermic.  CH4(s) + 2O2(g) → CO2(g) + 2H2O(l) Δ H° = -890 kJExothermic  2HCl(g) → H2(g) + Cl2(g) Δ H° = 185 kJEndothermic  4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l) Δ H° = -1169 kJ Exothermic  2.When potassium nitrate dissolves in water, the beaker containing the solution gets cooler. Is dissolving this salt an exothermic or an endothermic process?  This is an endothermic process. The reaction requires heat, which it absorbs from the surroundings (the water). This causes the water temperature to decrease.

15.  Assignment 1.1.1