Exothermic And Endothermic Reaction

An exothermic reaction is a chemical reaction that              

releases energy in the form of heat.

Expressed in a chemical equation:

reactants → products + energy

For an exothermic reaction, this gives a negative value for ΔH, since a larger value (the energy released in the reaction) is subtracted from a smaller value (the energy used for the reaction). For example, when hydrogen burns:

2H₂ + O₂ → 2H₂O

H = −483.6 kJ/mol of O₂                                                                                                      

Examples of exothermic reactions

• Combustion reactions of fuels
• Neutralization reactions such as direct reaction of acid and base
• Adding concentrated acid to water
• Burning of a substance
• Adding water to anhydrous copper(II) sulfate
• The thermitereaction
• Reactions taking place in a self-heating can based on lime and aluminum
• The setting of cementand concrete
• Many corrosion reactions such as oxidation of metals
• Most polymerisation reactions
• The Haber-Bosch process of ammonia production

                                                                                                              

An endothermic reaction is a chemical reaction that          

absorbs in the form of heat.

Expressed in a chemical equation:

reactants + energy → products

 For an endothermic reaction,   this gives a positive value for ΔH, since a larger value (the energy absorbed in the reaction) is subtracted from a smaller value (the energy used for the reaction).

Some examples of endothermic processes are:^[2]

• A chemical cold pack consisting primarily of ammonium nitrate and water.
• Evaporation of water
• Photosynthesis

 

Enthalpy Calculations

So today we did some notes on enthalpy calculations. It is  a measure of the total energy of a thermodynamics system. It includes the internal energy. Which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure. Delta H is the energy change in the reaction in the kJ/mole. The enthalpy of a system is defined as: H= U + pV

This is a video that will help u understand how to calculate Delta H in some enthalpy problems: http://www.youtube.com/watch?v=NoRg7eGfb9k

Types of Chemical Reactions

    So last day we did a lab on types of chemical reactions, the types of reaction we did were synthesis, decomposition, single replacement and double replacement. So the purpose of the lab was just to observe how different chemical reactions work. We don't really have much trouble during the lab because the procedures were well written.

   I also found a link which could help us all to know more about the types of chemical reactions

http://www.youtube.com/watch?v=tE4668aarck