Energetics

Basics of Energetics

• Chemistry often involves energy changes, which occur during chemical reactions.
• These changes are referred to as energetics.
• Energetics concerns the study of energy transfer in chemical reactions.

Exothermic and Endothermic 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 Transfer and Chemical Bonds

• 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.

Enthalpy Changes

• 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.

Hess’s Law

• Hess’s law states that the total enthalpy change for a reaction is the same no matter what route is taken.
• Hess’s law can be used to determine the enthalpy change of reactions that are difficult to measure directly.

Chemical Energy and Efficiency

• 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.

Activation Energy

• 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.