Energy is a concept.� Most definitions of the word energy fail to provide its exact meaning when applied to scientific matters.� In science the word energy is a concept that expresses two measurable properties, heat and work.� Here is the relationship of energy, heat and work: Energy Released=Work Done + Heat Released
The Law of Conservation of Energy, derived from centuries of observation and measurement, indicates that energy cannot be created or destroyed. But energy need not stay in one place. Energy can be converted from one form to another and can be created in one place and show up in another. Remember that energy, in an open system, can do work on the surroundings or supply heat to the surroundings.�
When we express energy as the sum of heat and work, we are making a very specific claim concerning these two properties. They are related. The relationship between heat and work is a close one, so close the amount of heat and the amount of work must be expressed with numerical values having the same units. Within limits, energy may be controlled to appear as heat (as we use electric power to dry clothes in a dryer) or work (the same electric power rotating the drum in the same dryer). Briefly, we define the amount of heat and/or work using two units, the Joule (J), and the calorie. The Joule and the calorie are related as follows: 1 cal = 4.184J
Both units represent quite small increments of energy. We must add 1 calorie of heat to increase the temperature of 1g of water 1 degree Celsius. Our bodies expend about 1J of work with a single heartbeat. For convenience sake, both the Joule and calorie are often expressed in multiples of 1000. We speak of the kilojoule (kj): 1 kJ = 1000J
and the kilocalorie (kcal).
1 kcal = 1000 cal
Thus we must add 4.184 kJ of heat to raise the temperature of 100g of water 10 degrees Celsius. Chemical Reactions and the Production of Energy Heat and Work We learned the foundation of...