chemical systems establish equilibrium when they balance the rates of their forward and reverse reactions but what happens when that equilibrium is Disturbed chemical systems like people will always try to establish equilibrium for people equilibrium implies a balance with the stress we experience and the support systems we have around us hopefully we get a good night's sleep spend time with friends and family attend school and study Etc but at some point a new stress may be thrown our way perhaps we catch a cold and become ill when this happens our equilibrium must shift to accommodate this change perhaps because of our illness we sleep more than usual spend less time at school and in general practice better self-care once we're healthy again our equilibrium will return to its original balance we all have many stresses in life and our equilibrium is constantly adjusting to help us live our best lives in chemistry reaction systems at equilibrium will face stressors of their own the concept of a chemical system shifting to alleviate the effect of stress on the system is called later's principle which in general states that chemical systems like us respond to stress by shifting or altering to alleviate that stress what is stress on a chemical system there are three that we will consider there are changes in concent ation changes in temperature and changes in pressure in this video we'll break down how chemical systems adapt to each of these stressors and further our understanding of the sher's principles we'll start by examining the effect of changing concentration on a chemical reaction let's take a look at the decomposition of hydrogen iodide into hydrogen and iodine gas remember that a chemical system will always respond to negate or alleviate the stress or change that occurs so for example if hydrogen iodide is added to the system the system equilibrium will respond in a way that reduces the hydrogen iodide therefore the system will shift to the right toward the product side in more hydrogen and iodine gas will form remember the reaction can also proceed in the reverse Direction so if iodine is added to the system the system will again respond by reducing the amount of iodine to alleviate the stress the system will shift to the left toward the reactants and more hydrogen iodine will form in general we can say that when a substance is added a chemical system will shift away from that addition if a product or reactant is removed from the system the chemical system will respond to replace the substance removed for example if hydrogen gas is removed the system equilibrium will shift to produce more hydrogen gas therefore the amount of hydrogen iodide in the system will decrease as a result changes in pressure will only affect chemical systems that contain gases as products or reactants remember that solids and liquids are virtually incompressible so pressure change does not affect them therefore when evaluating systems for effects due to changes in pressure substances appearing in the solid liquid or aquous state of matter are not considered in a sense pressure changes can be viewed as changes in concentration as concentration in this context is a measure of how many gas particles are in a given space we can increase pressure by compressing the gas or by adding an inert gas to The Container this will in turn increase concentration of each gas as there will be a larger ratio of the number of particles to the available space in contrast we can decrease pressure by expanding the container or by removing an inert gas this will decrease the concentration of each gas when evaluating a system for the possible effects due to pressure changes begin with two considerations one are gases present in the system remember that without gases there would be no effect for changing pressure if there are gases what are the high pressure and low press sides of the system or more simply which side of the reaction has more moles of gas we'll see how this makes an impact in just a bit let's take a look at the hab process which is the uction of ammonia from hydrogen and nitrogen gas changes in pressure will affect this system we know this because there are gases present in the reaction and there's an imbalance of the number of moles of gas on the reactant and product side without an imbalance we again would not see the impact of changing pressure on the system in this case the reactant side is the high press side of the equation with four moles of gas coming from the one mole of nitrogen and three moles of hydrogen the product side is the low pressure side with only two moles of gas coming from the two moles of ammonia note that more moles of gas imply more gas molecules and therefore more molecular collisions I.E more pressure let's examine the effects of changing the pressure of the system first we'll expand the container's volume as we previously saw this will decrease the overall concentration of the gas in our system to alleviate this change the system will shift to the left the production of reactants will produce the most moles of gas and therefore be the most effective way to increase the pressure of the system alternatively we can add an inert gas such as helium to the system at equilibrium adding a gas that does not take part in the reaction will cause an increase in the concentration of gases causing more collisions and thereby increasing the pressure the system will respond by shifting to the side with lower pressure which is the side with few fewer moles of gas this means the reaction will shift right toward the production of more ammonia producing more ammonia here results in a net loss in the number of gas particles in the container as for every four moles of nitrogen and hydrogen that are consumed only two moles of ammonia are made the final stress to a chemical system in equilibrium is a change in temperature when considering how changes in temperature will affect a system we have to consider the differences between an endothermic and exothermic reaction remember that if the enthalpy of the reaction shown as Delta H is greater than zero the reaction is considered endothermic endothermic reactions take in heat energy from their surroundings therefore we can write heat into the reaction as a reactant if Delta H is less than zero the reaction is considered exothermic exothermic reactions release heat energy into their surroundings therefore we could write heat into the reaction as a product keep in mind if the temperature is elevated the molecules will move more quickly therefore the overall energy will increase likewise if the temperature is lowered the molecules will move more slowly decreasing the system's energy as with our previous stressors a system in equilibrium will respond to alleviate a change in temperature let's look at the decomposition of P3 into PCL 3 and O2 if this system is cooled how will it respond will the amount of products increase or decrease because Delta H is positive we know that the forward reaction is endothermic meaning we can rewrite the reaction to include heat as a reactant which will allow us to predict shifts in equilibrium in a similar way to our previous stressors if the temperature is cooled the system's overall energy in equilibrium decreases therefore the system will respond by trying to increase inre its overall energy since the energy of an endothermic reaction is an input or is shown on the reactant side the system will shift to the left to make more reactants this also means the amount of products made at equilibrium will decrease let's contrast this with the hab process how will this reaction system respond to being cooled well this process is exothermic which we can tell by its negative Delta H value this means we can rewrite this equation to include Heat as a product if temperature is cooled the system will respond to produce more heat and will therefore shift the reaction to the right and the production of more products changing temperature will ultimately have the largest impact on our system as it changes the energetics of our particles as a result changing temperature will permanently change the value of the equilibrium constant k something that changing the other factors simply will not do in summary equal equilibrium is a dynamic state in which the rates of the forward and reverse reactions are equal the constant movement of atoms and molecules underpins this balance just as life presents us with challenges chemical systems experience stressors including changes in concentration pressure and temperature these systems adapt to regain balance in a process Guided by later's principles where adding a substance to a reaction will cause the reaction to shift away from that substance and removing a substance will cause a reaction to shift towards the substance that was removed remember understanding equilibrium in this way empowers us to predict and influence chemical reactions much like the equilibrium we strike in our Dynamic lives to maintain balance amid life's challenges