energy -energy transformations

Solution
The energy transformations of a coal fired power plant

Solar -------> Chemical potential --------> heat --------> kinetic----> electrical
Photosynthesis is the process that traps solar energy and converts it into chemical potential energy. This energy is stored in plant matter and is released as heat energy when coal is burnt. This heat is used to turn water into steam. The steam(water) molecules have a great deal of kinetic energy(they move very fast). This kinetic energy is used to turn the turbines that spin the generators producing electrical energy..

The energy transformations of a hydro-electric power plant

Solar-----> gravitational potential----->kinetic---->electrical

Water in the oceans of the world absorb solar heat energy. This heat energy causes the evaporation of many billions of tons of water around the world. The resultant water vapour rises high into the atmosphere where it condenses back into water and falls as rain. This water is trapped in man-made dams and used to turn huge turbines that spin the generators to create electrical energy.

Click to hide solution

Photosynthesis

The thermochemical equation above shows that the process of photosynthesis is an endothermic reaction. Energy is absorbed from the surroundings and transformed into chemical potential energy in the bonds of the product molecules. The source of energy for this reaction is the Sun.

The equation tells us that for evey 6 mole of carbon dioxide that reacts with 6 mole of water 2803 kilojoules of energy is needed.

The process of respiration is simply the reverse of photosynthesis. Respiration is an exothermic reaction with the release of heat energy. The reaction is shown below.

The burning of wood releases the energy trapped by photsosynthesis.This energy is present in the chemical bonds of the molecules that form wood. The reaction taking place when wood is burnt is the reverse of photosynthesis. So the reaction is exothermic. Notice the negative sign on the energy value of the respiration reaction above. Also notice how the energy value is the same in magnitude as that of photosynthesis.

Hide this information

Energy transformations
We know that energy can not be created or destroyed but it can change from one form into another. We see examples of such transformations every day. We will now try some exercises.
All energy on Earth has originated from the Sun. We change the many forms of energy into electrical energy to drive our modern cities and to maintain our standard of living. There are many different types of power stations, two of which are coal fired and hydro-electric power plants. Although both coal-fired and hydro-electric power plants use generators to produce electricity it is the method each uses to spin the turbines driving the generators that is different.

Consider the animation above, showing the process of photosynthesis. This is a process that requires energy in order to proceed. It is therefore said to be endothermic. 1) Where does the energy to drive the process of photosynthesis come from? 2) What type of energy is solar energy converted into? 3) What is the advantage of chemical energy over solar energy? 4) How is energy passed on from organism to organism in a food chain?
5) The chemical word equation for photosynthesis is given below water + carbon dioxide + energy => sugar + oxygen. The sugar is used by the plants as food and as a structural material to from wood. We burn would to release its energy and the chemical equation for this reaction is given below. sugar + oxygen.=> water + carbon dioxide + energy i) Where does the heat energy given off when burning wood come from ? ii) What is the ultimate source of the heat energy given off when burning wood ?
Continue