energetics

• • Chemistry often involves energy changes, which occur during chemical reactions.
• • Energetics concerns the study of energy transfer in chemical reactions.
• • A chemical reaction that releases energy to the surroundings is called an exothermic reaction. Combustion is an example.
• • A endothermic reaction absorbs energy from the surroundings. Photosynthesis is an example.
• • In an exothermic reaction, the energy required to break bonds is less than the energy released when new bonds are formed.
• • In an endothermic reaction, the energy required to break bonds is greater than the energy released when new bonds are formed.
• • Energy is needed to break chemical bonds, and energy is released when new bonds are formed.
  • The energy difference between the energy taken in to break bonds and the energy given out when new bonds are formed is the energy change of the reaction.
• • The enthalpy change (ΔH) of a reaction is the amount of energy absorbed or released by the reaction. It can be exothermic (negative ΔH) or endothermic (positive ΔH).
  • The enthalpy change for a reaction can be calculated from the energies needed to break bonds and the energies released in forming new bonds.
• Measuring Energy Changes

  • Energy changes in a chemical reaction can be measured in an insulated container, like a polystyrene cup.
  • The change in temperature can be used to calculate energy changes, using the formula q=mcΔT, where q is the heat transferred, m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature.
• • Not all of the energy released in an exothermic reaction can be used. Some energy is always wasted.
  • Energy efficiency can be improved by insulating reaction vessels, making the process quicker or using a catalyst.
  • Understanding and improving the efficiency of energy use is essential for sustainable development.
• • The activation energy is the minimum energy needed for a reaction to occur.
• • A reaction will not take place unless the particles collide with energy equal to or greater than the activation energy.
• • Catalysts increase the rate of chemical reactions by providing an alternative reaction pathway with a lower activation energy.