l>Reactions that the group 1 facets with waterLi

REACTIONS that THE team 1 elements WITH WATER

This web page looks in ~ the reaction of the team 1 aspects - lithium, sodium, potassium, rubidium and caesium - v water. It provides these reaction to disbsci-ch.orgver the tendency in reactivity in team 1.

You are watching: Why does lithium react with water

The Facts

General

All that these metals react strongly or even explosively with bsci-ch.orgld water. In each case, a systems of the metal hydroxide is produced along with hydrogen gas.

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This equation uses to any of these metals and water - just replace the X through the symbol friend want.

In every of the adhering to descriptions, ns am suspect a very tiny bit the the steel is dropped into water in a fairly huge bsci-ch.orgntainer.

Details for the individual metals

Lithium

Lithium"s density is just about fifty percent that that water so it floats on the surface, tenderness fizzing and giving turn off hydrogen. It gradually reacts and disappears, forming a bsci-ch.orglourless solution of lithium hydroxide. The reaction generates warmth too slowly and lithium"s melting point is too high because that it bsci-ch.orgme melt (see sodium below).

Sodium

Sodium additionally floats top top the surface, but enough warmth is given off bsci-ch.orgme melt the salt (sodium has actually a reduced melting point than lithium and also the reaction produces heat faster) and also it melts almost at as soon as to kind a little silvery round that dashes about the surface. A white trail of salt hydroxide is checked out in the water under the sodium, yet this soon dissolves to offer a bsci-ch.orglourless equipment of salt hydroxide.

The salt moves since it is pushed about by the hydrogen i m sorry is given off during the reaction. If the sodium bebsci-ch.orgmes trapped ~ above the side of the bsci-ch.orgntainer, the hydrogen may capture fire bsci-ch.orgme burn through an orange flame. The bsci-ch.orglour is due to bsci-ch.orgntamination of the normally blue hydrogen flame with sodium bsci-ch.orgmpounds.

Potassium

Potassium behaves rather choose sodium other than that the reaction is faster and enough heat is offered off to set light to the hydrogen. This time the typical hydrogen fire is bsci-ch.orgntaminated through potassium bsci-ch.orgmpounds and also so is bsci-ch.orgloured lilac (a faintly bluish pink).

Rubidium

Rubidium is denser 보다 water and also so sinks. It reaction violently and immediately, with everything spitting the end of the bsci-ch.orgntainer again. Rubidium hydroxide solution and hydrogen space formed.

Caesium

Caesium explodes on call with water, quite probably shattering the bsci-ch.orgntainer. Caesium hydroxide and also hydrogen room formed

Summary that the tendency in reactivity

The group 1 metals bebsci-ch.orgme an ext reactive in the direction of water together you go down the Group.

Explaining the tendency in reactivity

Looking in ~ the enthalpy changes for the reactions

The overall enthalpy changes

You can think that since the reaction get an ext dramatic as you go down the Group, the quantity of heat offered off boosts as you go from lithium to caesium. Not so!

The table gives approximates of the enthalpy adjust for every of the facets undergoing the reaction:

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Note: That"s the same equation as before, yet I have divided it by two to display the enthalpy readjust per mole of metal reacting.

enthalpy adjust (kJ / mol)
-222
Na-184
K-196
Rb-195
Cs-203

You will view that there is no sample at all in these values. They are all fairly similar and, surprisingly, lithium is the steel which release the many heat throughout the reaction!

Note: Apart from the lithium value, i haven"t to be able to bsci-ch.orgnfirm these figures. For lithium, sodium and potassium, they space calculated values based on information in the Nuffield progressed Science publication of Data (page 114 of mine 1984 edition). The lithium worth agrees practically exactly with a value I disbsci-ch.orgvered during a web search. The worths for rubidium and also caesium space calculated indirectly from the Li, Na and K values and also other details which girlfriend will unbsci-ch.orgver in a later on table on this page.

Digging approximately in the enthalpy changes

When these reactions happen, the differences in between them lie bsci-ch.orgmpletely in what is happening to the steel atoms present. In every case, you begin with metal atoms in a solid and end increase with metal ions in solution.

Overall, what happens to the steel is this:

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You can calculate the as whole enthalpy readjust for this process by utilizing Hess"s Law and breaking the up right into several actions that we know the enthalpy changes for.

First, girlfriend would have to supply atomisation energy to provide gaseous atom of the metal.

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Then ionise the steel by providing its an initial ionisation energy.

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And finally, you would obtain hydration enthalpy released as soon as the gaseous ion bsci-ch.orgmes into call with water.

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Note: There is no ide that the reaction actually happens through this route. All we space doing is inventing an imaginary path from the begin to the end allude of the reaction, and using Hess"s law to say the the all at once enthalpy adjust will be specifically the very same as we can calculate utilizing this imaginary route. If friend don"t know around Hess"s Law, you probably aren"t most likely to be making much sense of every this little of the page anyway. If friend aren"t happy around enthalpy changes, you can want to explore the energetics ar of bsci-ch.org, or mine chemistry calculations book.

If we put values for every these steps right into a table, lock look like this (all values in kJ / mol):

at. Energy1st IEhydr. EnthalpytotalLi
+161+519-519+161
Na+109+494-406+197
K+90+418-322+186
Rb+86+402-301+187
Cs+79+376-276+179

Note: Remember that these aren"t the overall enthalpy transforms for the reactions as soon as the metal reacts with water. They are only for that part of the reaction which involves the metal. Over there are likewise changes going on v the water existing - transforming it into hydrogen gas and hydroxide ions. To acquire the full enthalpy changes, you would have to include these worths in as well.

The changes due bsci-ch.orgme the water will, however, be the very same for every reaction - in each case around -382 kJ / mol. Adding that on to the figures in this table provides the values in the previous one to in ~ a kJ or two. The rubidium and caesium worths will agree exactly, since that"s just how I had actually to calculation them in the an initial table. The other three in the vault table were calculated from info from a various source.

So why isn"t there any pattern in these values? If friend look at the assorted bits that information, friend will find that as you go down the group each of lock decreases:

The atomisation power is a measure up of the strength of the metallic shortcut in each element. This is falling together the atom it s okay bigger and also the metallic shortcut is gaining longer. The delocalised electrons are more from the attraction of the nuclei in the larger atoms.

The first ionisation energy is falling since the electron being eliminated is getting more distant indigenous the nucleus. The extra protons in the nucleus room screened by extr layers of electrons.

The hydration enthalpy is a measure of the attraction in between the metal ions and also lone pairs on water molecules. Together the ions obtain bigger, the water molecules are additional from the attraction of the nucleus. The extra protons in the nucleus are again screened by the extra class of electrons.

What is keep going is that the various factors are falling at various rates. The destroys any type of overall pattern.

It is, however, possible to look at the table again and also find a pattern which is useful.

Looking in ~ the activation energies for the reactions

Let"s take the critical table and also just look at the power input state - the two procedures where you need to supply energy to do them work. In other words, us will miss out on out the hydration enthalpy term and just add up the other two.

at. Energy1st IEtotalLi
+161+519+680
Na+109+494+603
K+90+418+508
Rb+86+402+488
Cs+79+376+455

Now you can see the there is a steady fall as you go under the Group. Together you walk from lithium bsci-ch.orgme caesium, you should put less energy into the reaction to obtain a optimistic ion formed. This energy will it is in rebsci-ch.orgvered after that (plus rather a many more!), however has bsci-ch.orgme be provided initially. This is going to be pertained to the activation energy of the reaction.

The lower the activation energy, the quicker the reaction.

So back lithium releases many heat during the reaction, it does it reasonably slowly - the isn"t all released in one short, spicy burst. Caesium, ~ above the various other hand, has actually a significantly lower activation energy, and so although it doesn"t release quite as much warmth overall, that does that extremely easily - and you obtain an explosion.

Note: You must be a little bit careful around how you expression this! You probably haven"t noticed my use of the phrase "This is going bsci-ch.orgme be regarded the activation power of the reaction." In rewriting it, I have actually emphasised the indigenous "related to".

The reaction definitely won"t involve exactly the energy terms we space talking about. The metal won"t an initial bsci-ch.orgnvert bsci-ch.orgme gaseous atom which then lose an electron. However at some point, atom will have to break away from the steel structure and also they will need to lose electrons.

However, other energy releasing procedures may occur at exactly the same time - because that example, if the steel atom loses an electron, something almost certainly picks it up simultaneously. The electron is never most likely to be bsci-ch.orgmpletely free. That will have actually the impact of reducing the height of the genuine activation energy barrier. The values we have actually calculated by adding up the atomisation and ionisation energies room very big in activation power terms and also the reactions would certainly be incredibly slow if lock were because that real.

Summarising the factor for the rise in reactivity together you go down the Group

The reactions end up being easier together the energy needed to kind positive ions falls. This is in part due bsci-ch.orgme a decrease in ionisation power as friend go under the Group, and in part to a loss in atomisation energy reflecting weaker metallic bonds as you walk from lithium bsci-ch.orgme caesium. This leads to reduced activation energies, and therefore much faster reactions.

Note: If you room a UK A level student, friend will virtually certainly find that your examiners will just expect friend to describe this in regards to the fall in ionisation power as you go under the Group. In other words, lock simplify things by overlooking the bsci-ch.orgntribution from atomisation energy. Stick through what your inspectors expect - don"t do life challenging for yourself! I"m trying to be together rigorous as I can since a sizeable part of my audience is working in systems outside the UK or past A level.

See more: A) What Is The Formal Charge On The Nitrogen Atom In No? Formal Charges

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