Stressor

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For the medical use of this term, see Stress (medicine).

In chemistry, a stressor is something that either speeds up a reaction rate or keeps the reaction rate the same. Stressors include light, temperature and elevated sound levels. Stressors also include the phenomena of substance concentration (does not shift equilibrium), catalysis, substance surface area (speeds up the reaction rate), and the nature of the reactants.

In accordance with Le Chatelier's Principle, reactions shift away from stressors. For example, see the following equilibrium reaction. There are three distinct species: CO, H₂ and CH₃OH.

CO + 2H₂ ↔ CH₃OH

If the concentration of any of these species is changed, the reaction will shift accordingly. If [CO] is increased, the reaction will progress towards the products. If [CH₃OH] is increased, the reaction will progress towards the reactants.

Equilibrium is a dynamic process with forward and reverse reactions occurring simultaneously. When the two are in balance, the reaction appears complete.
Reaction rate describes how rapidly a chemical change takes place.

In organismal biology, a stressor is an external state change (such as a change of temperature or salinity) that results in a physiological response from an organism required to maintain homeostasis. Many organismal traits are occult until revealed by observing responses to stressors; this is particularly true of microorganisms.

[edit] As events that provoke stress.

In the field of environmental science and global environmental change there is concern about multiple stressors that impact on people's livelihoods. Climate change may be an important factor in increasing people's vulnerability but it is the combination of a change in climate with other stressors (such as changing pressure from land degradation, recurrent experiences, such as drought, and sudden shocks, such as floods and landslides) that will determine how the stressor can be coped with. The impact of these stressors create multiple stresses that are specific to the agent or system.

[edit] A definition for a stressor is:

An event or context that elevates adrenaline and triggers the stress response because it throws the body out of balance and forces it to respond; for example:

environmental stressors (elevated sound levels, over-illumination, overcrowding)
daily stress events (e.g. traffic, lost keys)
life changes (e.g. divorce, bereavement)
Workplace stressors (e.g. role strain, lack of control)

A stressor can also be an event that provokes stress.