What is Chemistry: Definition and 993 Discussions

Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant chemistry (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the properties of the soil on the moon (cosmochemistry), how medications work (pharmacology), and how to collect DNA evidence at a crime scene (forensics).
Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are two types of chemical bonds: 1. primary chemical bonds e.g covalent bonds, in which atoms share one or more electron(s); ionic bonds, in which an atom donates one or more electrons to another atom to produce ions (cations and anions); metallic bonds and 2. secondary chemical bonds e.g. hydrogen bonds; Van der Waals force bonds, ion-ion interaction, ion-dipole interaction etc.

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  1. G

    Determine all of the Physical Chemistry Variables of the System

    Homework Statement A weather balloon is filled with Helium gas and released from the ground. It goes up 18km and achieves a diameter of 15m. Determine if the following values are greater than zero, less than zero, or equal to zero: ΔV, ΔP, ΔT, ΔU, ΔH, Ssys, surr, Stot Homework Equations ΔU =...
  2. 655piano

    Chemistry Chemistry or Physics? Advice for Senior in High School

    I'm a senior in high school and very interested in both chemistry and physics. I have a strong background in chemistry but I am starting to lean more towards a career in physics. Any advice for college classes or decision making?
  3. S

    Organic Chemistry: Aromaticity

    Homework Statement Homework Equations Huckel's Rule: 4n +2 pi electrons The Attempt at a Solution I'm having problems with the last molecule. I said that the first molecule was indeed aromatic because it has 6 pi electrons and obeys the 4n + 2 rule. The second one is not aromatic because...
  4. X

    What is the specific activity of the air inside the sealed warehouse?

    Can anyone please guide me how to find solution of this problem A 0.2-g sample of 85Kr gas, which decays into stable 85Rb, is accidentally broken and escapes inside a sealed warehouse measuring 40×30×20 m. What is the specific activity of the air inside?
  5. J

    In absolute need of help with chemistry labs

    I just got out of my chemistry lab class at school, and needless to say, I don't think I am going to get a good grade. Basically, I felt like a complete idiot today. My professor was getting frustrated with me because he thinks I wasn't listening to him (even though I was). I never in my life...
  6. Elvis 123456789

    Grams of solute needed to lower vapor pressure of solvent?

    Homework Statement Some KCl is dissolved in water at 25°C, where it completely dissociates. The vapor pressure of pure water at 25°C is 28.3 mmHg. Estimate the mass in grams of KCl needed per liter of pure water to reduce the vapor pressure of water at 25°C by 5%. Homework EquationsThe Attempt...
  7. S

    Solid State Chemistry Question Regarding Fermi Energy

    Hi there, I am new to electron theory, and have a question regarding fermi energy. The book I am reading plots the Fermi energy distribuiton function vs Energy for T=0 ( upper right graph in pcture) and for T not equal to zero. The book says that, when T does not equal zero, the decrease in the...
  8. S

    Organic Chemistry - Synthesis of Lidocaine

    In lab we had to synthesize lidocaine, and one of the steps involved reacting a-chloro-2,6-dimethylacetanilide with diethylamine to form lidocaine. My professor told us that diethylamine-HCl crystals would form and these would help us determine the lidocaine yield (since they form at a 1:1 mole...
  9. K

    When does resonance take place?

    As in what are the conditions for resonance (i.e. in oganic chemistry) to occur? Sometimes it occurs, sometimes it doesn't; for reasons unknown. A little help please? :/:olduhh:
  10. A

    Find the Molarity of a Solution Using Concentrated Ammonia (28% by Mass)

    Homework Statement Calculate the molarity of a solution made by adding 35.5 mL of concentrated ammonia (28.0 % by mass, density 0.880 g/mL) to some water in a volumetric flask, then adding water to the mark to make exactly 250 mL of solution. (It is important to add concentrated acid or base...
  11. J

    Atmospheric Temperature and Air Molecule Density Calculation

    Homework Statement At an altitude of 50 km, the average atmospheric temperature is 0C. what is the average number of air molecules per cm^3 of air at this atmosphere? Given formula: P(sub h) = P(sub 0) x e^(-Mgh/RT) = -(Mgh x 10^5)/2.303RT Assuming P = 1 atm at sea level and h in km...
  12. kelsey

    Programs Majoring in Chemistry & Physics: Guide

    i am looking for something that includes both chemistry and physics thank you
  13. Science2Dmax

    Does the amount of matter in the universe stay at a constant amount?

    I was wondering if matter stays at a constant amount. You cannot really destroy anything really because crushing it just turns it into smaller pieces of itself, decomposition turns matter int separate elements, vaporizing just turns matter into gas and burning is a combination of all of the...
  14. W

    Engineering Transfer to chemical engineering from BS in chemistry?

    Hi. I'm currently an undergraduate student studying for a BS in chemistry and doing pre-pharm courses (I wanted backup career). I've taken anatomy and orgo lectures and labs. What I enjoy from orgo class was that they give you a start and an end, you fill in the rest. I like problems that are...
  15. B

    In Gibbs Free Energy, why multiply -T?

    When you get the equation for the Gibbs free energy, why do you multiply -T? Can't you multiply just T? I thought about this and came up with an answer of my own, which goes like 'Because its Gibbs 'Free' Energy, when you have that free energy ( \Delta G >0) you have the energy to do...
  16. K

    Organic Chemistry Nomenclature

    Homework Statement Provide an acceptable name for the alkane shown below. Homework Equations N/A The Attempt at a Solution I never get these right but...my guess would be 2-dimethyl-5-butononane? My reasoning: the longest carbon chain has 9 carbons so the base name would be nonane, there...
  17. K

    Organic chemistry hybridization and bond angles

    Homework Statement Determine the hybridization of the atoms labeled A, B and C in the molecule and the bond angles around them. Homework Equations N/A 3. The Attempt at a Solution A. Normally, I would say it is sp3 for oxygen since there are 4 groups attached to it including the lone...
  18. S

    Grade 11 Chemistry Problem about a Nonreaction

    Homework Statement If there is a reaction, write out the chemical equation for Hg(NO3)2(aq) + CH3COONa(aq) Homework Equations N/A The Attempt at a Solution The answer says that there is no reaction. I have absolutely no idea why not.
  19. R

    Good Chemistry Videos Websites

    Can anybody link some good inorganic chemistry video websites for a high school apart from Khan Academy Lectures. I found PatrickJMT for Maths videos quite useful. For physics there were many, e.g DrPhysicsA, Doc Schuster videos etc. Usually there are some like chemistnate and ben chem videos...
  20. 8008jsmith

    What are the Steps for Solving Organic Chemistry Resonance Homework?

    Homework Statement https://s.yimg.com/hd/answers/i/582779fb3e0b4cecab74f7adb74ed84e_A.png?a=answers&mr=0&x=1422153107&s=7d575e72049bd930d0e263cbd57eff58 The Attempt at a Solution I have attempted to solve it. But I don't know what I'm doing wrong.
  21. N

    Programs Astro vs Chemistry for Physics Major

    Hi all. I'm a prospective physics major, hoping to either go into particle physics or condensed matter research or enter tech if research doesn't turn out to be for me. I was wondering which elective I should choose for next semester--astro 101 or Chemistry 1 or CS 1? Will chemistry help me with...
  22. J

    Engineering Transition from Physics to Engineering?

    Hi there! I'm currently pursuing a Bachelors of Science in Physics with minors in both Applied Math & Chemistry and am considering a career in engineering. Now, before all of you engineers jump my case about physics isn't engineering or whatever, please be mindful I'm here for help about my...
  23. montoyas7940

    Organic Chemistry IR and NMR problem solving

    Homework Statement I am trying to help my daughter determine the structure of this carbon compound. It has seven carbons, 14 hydrogens and one oxygen. The oxygen must be in a ketone group. Also each carbon is different (as indicated by the carbon 13 NMR). Homework Equations The Attempt...
  24. Charles Stark

    Would taking a chemistry class help with physics?

    Ah ha! So I was looking through the physics classes I will have to take and noticed a lot of topics dealing with atoms and the like. Would it benefit me to take the first installment of basic Chemistry? I don't want to take the lab portion just the lecture section if it would be a tremendous...
  25. M

    Organometallic Chemistry -- Multistep synthesis question

    1. Question Start with a organometallic (Benzene)M(Co)3see picture below) and React it with R- to get A, Then react A with I2 to get B and react A with H+ to get C. What is A,B and C? 3. Attempt at answering the question. I am not sure about the hapticity of Benzene. ? But i am prety sure...
  26. A

    What is the independent variable in Boyle's Law?

    I asked my teacher, and I was told that volume is the independent variable, and that pressure is dependent. The textbook I'm using said the same thing. After looking up some graphs of the law, I found that both pressure and volume were used as independent variables. It seems counter-intuitive...
  27. E

    Standarization of a Sodium Hyrdoxide Solution

    Homework Statement Hello, I missed a lab before the break because I was really sick and I need help. I was given the data from my partners for the titration lab and I don't understand how to calculate the amount of potassium hydrogen phthalate used in each trial, amount concentration of the...
  28. A

    How to Calculate Energy for Atmospheric Molecule Reaction and Isolate Gases?

    The atmosphere consists of two toxic, and unfortunately abundant gases in our atmosphere. Carbon dioxide and methane. Carbon dioxide produced by factories are not needed in the atmosphere and cause harm. So is methane. Acegikmoqsuwy and I thought of an equation to solve this problem: CH4 + CO2...
  29. Y

    Chemistry Recommendation for Chemistry textbooks

    I want a good book on Physical Chemistry at 11-12(university or pre-un) grade level. It should include topics about bonding(VSEPR, VBT, MO) etc. I also need suggestions about some books on organic and inorganic chemistry.
  30. G

    Divided between physics and chemistry

    They say one way to torture a person is to give them choices. I feel this is partly true in this case. I have a goal in mind for either one: if I do physics, I'll pursue nuclear physics/engineering but I go the chemistry route: I'll do biochemistry/forensic science. I've done a lot of research...
  31. J

    Procedure of preparation of HCl

    Homework Statement Knowing that HCl is strong acid we want to prepare HCl solution of pH=4.2.starting from a solution of pH=2.9.Explain briefly the procedure that should be followed to do this operation. Homework Equations pH=-log(H3O+) 3. The Attempt at a Solution [/B] I calculated: At...
  32. TheNerdConstant

    15 year old physics nerd bids everyone hello

    Hi I have been passionate about physics for the last 4 years self taught up to about the first year of university level. I have found this website because now, at this key point in my life i need the guidance and knowledge that people from scientific fields only posses. I am interested to meet...
  33. sunshine1025

    Food Chemist vs. Chemical Engineer- Help

    First, thank you for taking the time to read this. I need some guidance as I am inventing somewhat of a new edible product. Curious as to if someone can point me in the right direction for the type of chemist I should actually be looking for. At first I was under the impression that it would be...
  34. C

    Engineering Chemical Engineering at Uni A: Which Option is Better?

    I wanted to do chemical engineering at a particular uni but was ineligible to enter any of the engineering programs (lets call this uni A). I have 2 options since that uni A is the only uni in my location which offers chem eng. 1) Major in chemistry at uni A and take similar units as chem eng...
  35. N

    Beginner chemistry experiments

    I know there are many recourses online. But I'd like your individual input/advice What are some good chemical experiments I can do at home? Thanks
  36. A

    How do you solve this stoichiometry problem? Is it possible?

    10.25g of a compound, including chlorine is then diluted. So there is 10.25g in the original compound, which is then diluted. 30mL of that solution is combined with an excess of AgNO3 to create 35.5g of AgCl. What is the mass percent of chlorine in the original compound/sample. I got 8.78g for...
  37. N

    What topics should I review before taking Gen Chem 2?

    I'm planning on taking a second semester general chemistry course in the spring, and I'm wondering what I should study before hand. Based on RateMyProfessor, my teacher is going to be super hard. I took the first semester general chemistry course and I got an A in it, but that was last fall...
  38. AdityaDev

    Electrochemistry: reference electrode

    Reduction half reaction : Cu2++2e- -> Cu(s) I have a doubt in using the reference electrode. For example if I have the calomel electrode (ESCE=0.24V) how do I use it with the copper half cell? Are these reactions correct? Cu2++2e- -> Cu(s) 2Hg+2Cl -> Hg2Cl2+2e- To get Ecell=0.24+ECu|Cu2+
  39. D

    Questions about the intersection between chemistry & physics

    I am in some real need of advice on the possibilities of my future plans. A bit of background, 32 years old, went back to undergrad at 30 and currently enrolled in a Bsc (hons) degree in Natural Sciences in the UK with my major subject as Chemistry. Plans to give my full effort to getting into...
  40. gracy

    Which Type of Bond is Strongest in Chemistry?

    Strongest bond in chemistry ionic ,covalent or metallic?Bond strength decrease in the following order covalent > ionic > metallic so i think strongest bond would be covalent bonding then comes ionic bonding and at last metallic bonding.Correct me if i am wrong.One more question is water/ice...
  41. H

    AP Chemistry Chemical Kinetics Problem

    Homework Statement The rate of the reaction was studied at a certain temperature. O(g) + NO2(g) --> NO(g) + O2(g) In the first set of experiments, NO2 was in large excess, at a concentration of 1.0 * 10^ 13 molecules/cm3 with the following data collected. time (s) [O] (atoms/cm3) 0...
  42. Q

    What is the correct mechanism for saponification?

    Homework Statement Problem: I am told that the first mechanism is operative in saponification. The Attempt at a Solution However, this strikes me as wrong because the first mechanism involves the formation of dianion. Using hydroxide ion to abstract a proton and make that particular...
  43. A

    Does ethanol evaporate in dried food?

    I was wondering, if ethanol is used in a food, as it commonly is with food flavorings (as a solvent), and that food is then dried out such that It is made into a powder or cereal or something, does all the ethanol completely evaporate? I know ethanol is very volatile and has a low boiling...
  44. J

    Physical Chemistry pH question

    Homework Statement The dissociation constant Ka for the acid-base reaction HA-->(H+)+(A-) is given by Ka = products / reactants; but instead of listing Ka, people generally list pKa = -logKa (where log indicates the 10-base logarithm). Similarly, instead of using [H+], people generally use pH...
  45. H

    Geometry Optimization in Computational Chemistry

    I've read an article about computational chemistry in which the authors were performing a geometry optimization. For this purpose, they firstly optimized the geometry at HF/6-311++G(d,p) level with full relaxation on the potentiel energy surface (what does that mean exactly ? Can we extract this...
  46. B

    Programs Exploring a Career in Chemistry: Bachelor's or Master's?

    I majored in materials science and engineering, but my primary interest seems to be more in the chemistry aspect of materials, so I've been thinking about going into chemistry as well. I've taken chemistry courses (up to organic chemistry and orgo lab) but did not major in it. For chemistry PhD...
  47. C

    How Can We Solve this Second Order ODE for Electron Behavior?

    Homework Statement I'm taking an online introductory chem course, and while explaing the failure of classical mechanics to describe electron behavior, the teacher brought up the following ode which is based on Newton's second law and coulombs law: -e^2/4(pi)(epsilon-nuaght)r^2=m(d^2r/dt^2)...
  48. Ritzycat

    Chemistry vs Physics for Undergrad

    Hello, I have questions. I love science. I don't think I am much of a biology person so naturally I am more appealed to both chemistry and physics. While I find physics incredibly fascinating and logical, I am exceedingly mediocre at the subject, earning only B's on all of the quizzes and...
  49. K

    How Much Energy Is Needed to Decompose 765g of PCl3?

    Homework Statement How much energy is required to decompose 765 g of PCl3, according to the reaction below? The molar mass of PCl3 is 137.32 g/mol and may be useful. 4 PCl3(g) → P4(s) + 6 Cl2(g) ΔH°rxn = +1207 kJ The Attempt at a Solution 765 g PCl3 x 4 mol PCl3/137.32 g PCl3 = 22.28 mol...
  50. Ritzycat

    Guidance with some chemistry concepts

    Hello! I understand that a lot of this may be considered physics, but It is for AP Chemistry. We will likely be required to identify a certain element on the periodic table given a set of quantum numbers of one of its electrons. I understand the primary quantum number, n, essentially...
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