Chemical Changes and Reactions
A chemical reaction can occur by two means-
- Reactant+ Reagent → Product
- Reactant + Reagent → Intermediate → Product
A reaction can take place only when –
- The molecules collide among themselves.
- The energy of the reactants should cross the threshold energy by absorbing activation energy.
- The molecules should orient themselves in a proper orientation.
Conditions necessary for a chemical change-
Mixing or close contact-
- P4 + 6I2 → 4PI3
- Pb(NO3)2 + 2KI → 2KNO3 + PbI2
In molten state or in aqueous solution:
- (COOH)2 + Na2CO3 → (COONa)2 + CO2 + H2O
- NaCl + AgNO3 → AgCl + NaNO3
- Any double decomposition reaction.
Heat:
- NH4NO3 → N2O + 2H2O
- NH4NO2 → N2 + 2H2O
- 4HNO3 → 2H2O + 4NO2 + O2
- 2NaNO3 → 2NaNO2 + O2
- 2Ca(NO3)2 → 2CaO + 4NO2 + O2
- 2Zn(NO3)2 → 2ZnO + 4NO2 + O2
- 2Pb(NO3)2 → 2PbO + 4NO2 + O2
- 2Cu(NO3)2 → 2CuO + 4NO2 + O2
- 2AgNO3 → 2Ag + 2NO2 + O2
- Hg(NO3)2 → Hg + 2NO2 + O2
- ZnCO3 → ZnO + CO2
- CuCO3 → CuO + CO2
Light :
- 2AgNO3 → 2Ag + 2NO2 + O2
- 2H2O2→2H2O + O2
- H2 + Cl2 → 2HCl
- 2Cl2 + 2H2O →4HCl + O2
- CH4 + Cl2 → CH3Cl + HCl
Electricity:
- 2NaCl → 2Na + Cl2
- PbBr2 → Pb + Br2
- 2H2O → 2H2 + O2
Pressure:
- N2 + 3H2 2NH3 200 atm
- HgCl2 + 2KI → HgI2 + 2KCl
- C6H5Cl + NaOH → C6H5ONa + HCl
Catalyst:
Chemical substances which can increase or decrease the speed of a reaction but itself remain intact in its mass.
Positive catalyst:
Chemical substances which can increase the speed of a reaction but itself remain intact in its mass.
Preparation of | Reaction | Positive catalyst |
Ammonia(NH3) [Haber’s process] | N2 + 3H2 2NH3 | Fe |
Nitric Acid (HNO3 ) [Ostwald process] | 4NH3 + 5O2 →6H2O + 4NO | Pt |
Sulphuric acid(H2SO4) [Contact process] | 2SO2 + O2 → 2SO3 | V2O5 |
Ethane(C2H6) | C2H4 + H2 → C2H6 | Pt or Pd or Ni |
Chlorobenzene(C6H5Cl) | C6H6 + Cl2 → C6H5Cl + HCl | Fe |
Oxygen | 2KClO3 → 2KCl + 3O2 | MnO2 |
Hydrogen (Bosch Process) | (CO + H2) + H2O → CO2 + 2H2 | Fe2O3 |
Decomposition of hydrogen peroxide | 2H2O2 2H2O + O2 | Pt, Ag, Co, Fe, Cu, Au |
Negative catalyst:
Chemical substances which can decrease the speed of a reaction but itself remain intact in its mass.
Reaction | Negative catalyst | |
Decomposition of hydrogen peroxide | 2H2O2 2H2O + O2 | Glycerine, acetanilide, phosphoric acid, urea, alcohol |
Oxidation of chloroform | CHCl3 + O2 → COCl2 | Alcohol |
Promoters:
Chemical substances that increase the efficiency of the catalyst.
- Mo or Al2O3 acts as a promoter of Fe during Haber’s Process.
- Chromic oxide acts as a promoter of Fe2O3 during the Bosch Process.
Catalyst Poison:
Chemical substances that can decrease the efficiency of the catalyst.
PbSO4+ S+ Quiniline acts as a poison during the preparation of acetaldehyde from Acetyl chloride.CH3COCl + H2 → CH3CHO + HCl
Characteristics of Chemical Reactions:
Evolution of gas:
- Zn + 2HCl → ZnCl2 + H2 ↑
- Na2CO3+ 2HCl → 2NaCl + H2O + CO2↑
- Na2SO3 + 2HCl → 2NaCl + H2O + SO2↑
- Na2S+ 2HCl → 2NaCl + H2S↑
- MnO2 + 4HCl → MnCl2 + Cl2↑ + 2H2O
- 2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3↑
- Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2 ↑
Change of colour:
- Fe + CuSO4(Blue solution) → FeSO4 (Green solution)+ Cu(reddish brown residue)
- Zn + CuSO4(Blue solution) → ZnSO4 (Colourless solution)+ Cu(reddish brown residue)
Formation of precipitation:
Reaction | Colour of precipitation |
Pb(NO3)2 + 2HCl → PbCl2 ↓+ 2HNO3 | White |
Hg2(NO3)2 + 2HCl → Hg2Cl2 ↓ + 2HNO3 | White |
AgNO3 + HCl → AgCl ↓ + HNO3 | White |
BaCl2 + H2SO4 → BaSO4 ↓ + 2HCl | White |
Pb(NO3)2 + H2SO4 → PbSO4 ↓ + 2HNO3 | White |
CaCl2 + 2NaOH → Ca(OH)2 ↓+ 2NaCl | White |
ZnCl2 + 2NaOH → Zn(OH)2 ↓+ 2NaCl | Gelatinous white |
Pb(NO3)2 + 2NaOH → Pb(OH)2 ↓ + 2NaNO3 | Chalky white |
FeSO4 + 2NaOH → Fe(OH)2 ↓+ Na2SO4 | Dirty green |
FeCl3 + 3NaOH → Fe(OH)3 ↓+ 3NaCl | Reddish brown |
CuSO4 + 2NaOH → Cu(OH)2↓ + Na2SO4 | Pale blue |
CuSO4 + H2S→ CuS ↓+ H2SO4 | Black |
Change of state:
NH3 (g)+ HCl (g)→ NH4Cl(s)
Types of chemical reactions:
Synthesis or Direct combination:
Type of reaction where two or more substances combine to form a single product.
- NH3 + HCl → NH4Cl
- 2NO + O2 → 2NO2
- 2NH3 + H2SO4 → (NH4)2SO4
- 6NH3 + P2O5 + 3H2O → 2(NH4)3PO4
- N2 + 3H2 2NH3
- Pb + S → PbS
- Fe + S → FeS
- 2Fe + 3Cl2 → 2FeCl3
Decomposition:
The type of reaction where is compound is broken down into two or more elements or compounds.
Thermal decomposition:
The type of reaction where is compound is broken down into two or more elements or compounds by applying heat.
- NH4NO3 → N2O + 2H2O
- NH4NO2 → N2 + 2H2O
- 4HNO3 → 2H2O + 4NO2 + O2
- 2NaNO3 → 2NaNO2 + O2
- 2Ca(NO3)2 → 2CaO + 4NO2 + O2
- 2Zn(NO3)2 → 2ZnO + 4NO2 + O2
- 2Pb(NO3)2 → 2PbO + 4NO2 + O2
- 2Cu(NO3)2 → 2CuO + 4NO2 + O2
- 2AgNO3 → 2Ag + 2NO2 + O2
- Hg(NO3)2 → Hg + 2NO2 + O2
- ZnCO3 → ZnO + CO2
- CuCO3 → CuO + CO2
- MgCO3 → MgO + CO2
- 2Ag2CO3 → 4Ag + O2 + 2CO2
- (NH4)2Cr2O7→ Cr2O3 + 4H2O + N2
- Pb(OH)2 → PbO + H2O
- Zn(OH)2 → ZnO + H2O
- Ca(OH)2 → CaO + H2O
- Cu(OH)2 → CuO + H2O
- 4AgOH → 4Ag + O2 + 2H2O
Photochemical Decomposition:
The type of reaction where is compound is broken down into two or more elements or compounds by applying light.
- 2H2O2 → 2H2O + O2
- 2AgNO3 → 2Ag + 2NO2 + O2
Electrochemical Decomposition:
The type of reaction where is compound is broken down into two or more elements or compounds by passing electricity.
- 2NaCl → 2Na + Cl2
- PbBr2 → Pb + Br2
- 2H2O → 2H2 + O2
Displacement:
The type of chemical reaction where a more active element displaces a less active metal from its salt solution or aqueous solution.
- Zn + H2SO4 → ZnSO4 + H2
- Zn + CuSO4 → ZnSO4 + Cu
- Cl2 + 2KI → 2KCl + I2
- Fe + 2HCl → FeCl2 + H2
Double decomposition:
The type of reaction where the two compounds mutually exchange their radicals to form two new compounds in aqueous solution.
1.Precipitation Reaction:
The type of reaction where two compounds mutually share their radicals to form two compounds out of which one is an insoluble salt or precipitation in aqueous solution.
Reaction | Colour of precipitation |
Pb(NO3)2 + H2S → PbS ↓ + 2HNO3 | Black |
2AgNO3 + H2S →Ag2S ↓ + 2HNO3 | Black |
ZnSO4+ H2S →ZnS ↓ + H2SO4 | White |
Na2S2O3 + 2AgNO3 → Ag2S2O3↓+ 2NaNO3 | White → Yellow→Orange→Red→Brown→Black |
2. Neutralization Reaction:
The type of reaction where an acid reacts with a base to form salt and water only.
- NaOH + HCl →NaCl + H2O
- H2SO4 + 2NaOH →Na2SO4 + 2H2O
- HNO3 + NaOH →NaNO3 + H2O
3. Hydrolysis:
The type of reaction where a salt react with water to form an acidic or basic solution.
Reaction | Nature of the final solution |
Na2CO3 + 2H2O → 2NaOH + H2CO3 | Basic |
CH3COONa + H2O → CH3COOH + NaOH | Basic |
K3PO4 + 3H2O → H3PO4 + 3KOH | Basic |
NH4Cl + H2O → HCl + NH4OH | Acidic |
(NH4)2SO4 + 2H2O → H2SO4 + 2NH4OH | Acidic |
CuSO4 + 2H2O → H2SO4 + Cu(OH)2 | Acidic |
ZnSO4 + 2H2O → H2SO4 + Zn(OH)2 | Acidic |
FeCl3 + 3H2O → 3HCl + Fe(OH)3 | Acidic |
FeSO4 + 2H2O → H2SO4 + Fe(OH)2 | Acidic |
Exothermic Reaction:
The type of reaction where heat is produced.
- C + O2 → CO2
- CH4 + 2O2→CO2 + 2H2O
- CaO + H2O →Ca(OH)2
- N2 + 3H2 2NH3
Endothermic reaction:
The type of reaction where heat is absorbed.
- C + 2S → CS2
- N2 + O2 → 2NO
- NaNO2 + HCl → NaCl + HNO2
Reversible reaction:
The type of chemical reaction that can be reversed by changing the conditions of the reaction.
- 2SO2 + O2 2SO3
- N2 + 3H2 2NH3
- 3Fe + 4H2O + Fe3O4 + 4H2
Few Important Reactions:
Reaction | Observation |
2Zn(NO3)2 → 2ZnO + 4NO2 + O2 | When zinc nitrate is heated, a residue is formed which is yellow when hot and white when cold. A reddish brown gas is evolved. |
2Pb(NO3)2 → 2PbO + 4NO2 + O2 | When lead nitrate is heated, a residue is formed which is yellow when hot and cold. A reddish brown gas is evolved. |
2Cu(NO3)2 → 2CuO + 4NO2 + O2 | When copper nitrate is heated, a black coloured residue is formed. A reddish brown gas is evolved. |
ZnCO3 → ZnO + CO2 | When zinc carbonate is heated, a residue is formed which is yellow when hot and white when cold. A colourless gas is evolved which turns lime water milky. |
(NH4)2Cr2O7 → Cr2O3 + 4H2O + N2 | When orange coloured ammonium dichromate is heated, green coloured residue is formed. |
CuSO4.5H2O → CuSO4 + 5H2O | When blue vitriol is heated, a white anhydrous powdery solid is formed. |
CuCO3 → CuO + CO2 | When copper carbonate is heated, a black coloured residue is formed. A colourless gas is evolved which turns lime water milky. |
Few important observations:
Compound or element | Observation |
H2 gas | Colourless odourless gas which burns with a pop sound |
O2 gas | Colourless odourless gas which turns alkaline pyrogallol solution brown. |
CO2 gas | Turns lime water milky but have no effect on acidified orange potassium dichromate solution green. |
SO2 gas | i)Turns lime water milky ii)Turns acidified orange potassium dichromate solution green iii)Turns acidified pink potassium permanganate solution colourless. |
H2S gas | i)Rotten egg smell ii)Turns moist lead acetate paper black iii)Turns lead nitrate solution black. |
Cl2 gas | i)Greenish yellow gas ii) Turns moist starch iodide paper blue black |
HCl gas | i)Produce a dense white fumes when comes in contact with a glass rod dipped in NH4OH. ii)A curdy white ppt is formed when the gas is passed through silver nitrate solution. |
NH3 gas | i) Produce a dense white fumes when comes in contact with a glass rod dipped in conc.HCl. ii)Turns nessler’s reagent brown. |
Water vapour | i) Turns anhydrous copper sulphate blue from white. ii) Turns anhydrous cobalt chloride pink from blue. |
NO2 gas | i)Reddish brown gas ii)Turns acidified green ferrous sulphate solution brown. |
I have read several good stuff here. Definitely worth bookmarking for revisiting. I surprise how much effort you put to create such a wonderful informative site.
Simply desire to say your article is as amazing. The clearness in your post is simply great and i could assume you’re an expert on this subject. Well with your permission let me to grab your feed to keep updated with forthcoming post. Thanks a million and please carry on the rewarding work.
Hey! This is my 1st comment here so I just wanted to give a quick shout out and tell you I really enjoy reading your posts. Can you suggest any other blogs/websites/forums that cover the same topics? Thanks a lot!
Valuable info. Lucky me I found your website by accident, and I’m shocked why this accident did not happened earlier! I bookmarked it.
Attractive section of content. I just stumbled upon your site and in accession capital to assert that I acquire in fact enjoyed account your blog posts. Anyway I will be subscribing to your feeds and even I achievement you access consistently rapidly.
Hello. Great job. I did not anticipate this. This is a remarkable story. Thanks!
Well I definitely liked studying it. This subject offered by you is very useful for proper planning.
A powerful share, I just given this onto a colleague who was doing a bit analysis on this. And he in actual fact bought me breakfast because I discovered it for him.. smile. So let me reword that: Thnx for the deal with! However yeah Thnkx for spending the time to discuss this, I feel strongly about it and love studying more on this topic. If potential, as you turn into expertise, would you thoughts updating your blog with more particulars? It is extremely helpful for me. Huge thumb up for this weblog publish!
Nice blog here! Also your site loads up fast! What host are you using? Can I get your affiliate link to your host? I wish my site loaded up as fast as yours lol
I have been examinating out some of your posts and it’s pretty clever stuff. I will make sure to bookmark your site.
Thanks a lot for sharing this with all of us you really know what you’re talking about! Bookmarked. Please also visit my site =). We could have a link exchange arrangement between us!
Wow! Thank you! I constantly needed to write on my site something like that. Can I include a fragment of your post to my website?
Very well written post. It will be helpful to everyone who employess it, as well as me. Keep up the good work – for sure i will check out more posts.
What’s Happening i am new to this, I stumbled upon this I’ve found It positively useful and it has aided me out loads. I hope to contribute & aid other users like its helped me. Great job.
Its such as you learn my thoughts! You appear to know so much approximately this, such as you wrote the book in it or something. I believe that you could do with a few to force the message house a little bit, but instead of that, that is great blog. A fantastic read. I will certainly be back.
You made some decent points there. I looked on the internet for the problem and located most people will go along with along with your website.
I was recommended this blog by my cousin. I’m not sure whether this post is written by him as nobody else know such detailed about my difficulty. You are wonderful! Thanks!
I simply had to thank you so much again. I do not know what I might have taken care of in the absence of the type of ways contributed by you concerning my subject. It became an absolute alarming scenario for me personally, nevertheless understanding a professional manner you treated the issue took me to leap over happiness. Extremely happy for this advice and then expect you recognize what a great job you are carrying out instructing the rest all through your web blog. I am sure you haven’t got to know any of us.
I do agree with all the ideas you’ve presented in your post. They’re very convincing and will certainly work. Still, the posts are too short for newbies. Could you please extend them a little from next time? Thanks for the post.
I have fun with, cause I found just what I was looking for. You’ve ended my 4 day long hunt! God Bless you man. Have a great day. Bye
I do like the manner in which you have presented this particular problem and it does provide me personally some fodder for consideration. Nonetheless, from everything that I have observed, I only hope when the responses pack on that folks stay on point and don’t embark on a soap box of the news of the day. Anyway, thank you for this excellent point and while I do not agree with this in totality, I value your point of view.
Thank you for another informative web site. Where else could I get that kind of info written in such an ideal way? I have a project that I’m just now working on, and I’ve been on the look out for such info.
I don’t even know how I stopped up right here, but I believed this submit was good. I do not recognise who you might be but definitely you are going to a well-known blogger when you aren’t already 😉 Cheers!
I’m not sure where you’re getting your information, but great topic. I needs to spend some time learning more or understanding more. Thanks for magnificent information I was looking for this info for my mission.
I like what you guys tend to be up too. This kind of clever work and exposure! Keep up the fantastic works guys I’ve added you guys to my personal blogroll.
Hello! I know this is kinda off topic however , I’d figured I’d ask. Would you be interested in exchanging links or maybe guest authoring a blog article or vice-versa? My website goes over a lot of the same subjects as yours and I believe we could greatly benefit from each other. If you are interested feel free to shoot me an e-mail. I look forward to hearing from you! Superb blog by the way!
I don’t even know how I ended up here, but I thought this post was great. I do not know who you are but certainly you are going to a famous blogger if you aren’t already 😉 Cheers!
Comments are closed.