Chemistry

Introduction

Evaporation can be defined as the process where liquid water is transformed into a gaseous state. Evaporation can only occur when water is available. It also requires that the humidity of the atmosphere be less than the evaporating surface (at 100% relative humidity there is no more evaporation). The evaporation process requires large amounts of energy. For example, the evaporation of one gram of water requires 600 calories of heat energy. Transpiration is the process of water loss from plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmospheric and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process. Transpiration also transports nutrients from the soil into the roots and carries them to the various cells of the plant and is used to keep tissues from becoming overheated. Some dry environment plants do have the ability to open and close their stomata. This adaptation is necessary to limit the loss of water from plant tissues. Without this adaptation these plants would not be able to survive under conditions of severe drought.

Evaporation

It is often difficult to distinguish between evaporation and transpiration. So we use a composite term evapotranspiration. The rate of evapotranspiration at any instant from the Earth's surface is controlled by four factors: It takes about 600 calories of heat energy to change 1 gram of liquid water into a gas. The rate and quantity of water vapor entering into the atmosphere both become higher in drier air. Many of us have observed that our gardens need more watering on windy days compared to calm days when temperatures are similar. This fact ...