4b) Energetics

Exothermic reactions:
Energy is transferred from the reacting mixture to the surroundings and temperature of surroundings increases

Endothermic:
Energy is transferred from the surroundings to the reaction mixture and temperature of surroundings decreases

Copper cup experiment is a simple calorimetry experiment:

Paper Two - Molar Enthalpy:
Measure temperature change of the experiment
Then use this calculation - Energy, Q = mc∆T                  m= mass of surroundings (water or solution) ∆T = change in temp.
                                           or

                                           ∆H = Q/n                                  n = number of moles    sign - exo and + endo 

∆H is the change in heat energy 

Q is measured in Joules 

Simple Energy Level Diagram:

Exothermic

Endothermic 

Ea or activation energy is needed to break or make bonds

Bonds:

Breaking bonds puts energy in - endothermic, 

whilst making new bonds releases energy - exothermic

Paper Two - Using average bond energies to calculate the enthalpy change during a simple chemical equation:

You are given the reaction and table of data 

Then with the information work out the broken bonds (A) and the bonds you make (B)  

Then subtract them to get the ∆H 

2b) Group 1 elements

The group 1 elements are lithium, sodium and potassium

• They all react a similar way in water:

metal and water -------> metal hydroxide and hydrogen
2M(s)       2H2O(l)            2MOH(aq)                H2(g)

• alkali metals 
• reactive metals 
• shiny silver when freshly cut
• low density 
• low melting point 

Metal	Observations
Lithium (Li)	Fizzes, floats and moves on the water surface
Sodium (Na)	Fizzes, floats, forms a ball and moves around surface of water (may ignite)
Potassium (K)	Fizzes, reacts vigorously and burns with a lilac flame (sometimes explodes)

Summary: Group 1 elements get more reactive as the atomic number increases 

1. Atoms increase in size 

2. Outer electrons further from nucleus 

3. Therefore they are easily lost