How does a catalyst affect the net difference in energy between reactants and pr

Question

How does a catalyst affect the net difference in energy between reactants and products? Why do hydrogen peroxide solutions last longer when stored in brown bottles in the refrigerator' The directions on a commercially available bottle of hydrogen peroxide tell you to keep your fact from the bottle before opening it. What is the reasoning behind this safety precaution? What type of process is associated with breaking up the crystal lattice of an ionic compound? What factors determine how the temperature changes when dissolving an ionic compound it? Calculate the heat (in calories) liberated in the neutralization reaction shown below: Quantification in the Chem Lab I - Energy Transfer

Explanation / Answer

a) A catalyst provides an alternative route for the reaction to take place with a lower activation energy,so that the rate of the reaction increases .No change in net difference between the energy of product and reactants.

b)Hydrogen peroxide decomposes into H2O and O2 in the presence of light energy and so is wasted.It should be stored in dark to preserve.

H2O2-+ light àH2O +2O.

2O.-àO2

O2 is evolved as gas increasing the concentration of H2O,thereby diluting H2O2 and decreasing its efficiency.    

c)When H2O2 bottle is opened ,the O2 gas (3% or less ) formed due to its decomposition may make it spill straight away on your face due to increased gas pressure.

d)The crystal lattice of an ionic compound is made up of cations and anions held strongly by each other due to electrostatic forces of attraction.When an crystal lattice of an ionic compound is broken ,heat is absorbed.It is an endothermic process.

e)The charge on the cations and anions ,higher the charge ,higher the electrostatic attraction between the ions,stronger is the bond .More energy required to break the bond.

Also the size of the cation and anion,smaller the size ,more strongly the ions attract the electrons of the other one (nucleus is closer to the valence electrons of the other ion to attract it).

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