A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or alloys. Chemical elements may or may not be included in the definition, depending on expert viewpoint.Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical.
Chemical substances exist as solids, liquids, gases, or plasma, and may change between these phases of matter with changes in temperature or pressure and time. Chemical substances may be combined or converted to others by means of chemical reactions.
Forms of energy, such as light and heat, are not matter, and are thus not "substances" in this regard.
We do know that in the process of chemical reaction, atoms or molecules come closer, form bonds and get stabilized by sharing or donating electrons, thus filling the valance shell of atoms. But why do they want to get stabilized?.
Why when a chemical species is stablized by resonance, its energy level is lower? As I know, resonance is only a kind of electrons delocalization within the species. There is no interaction between that species and the environment.
Homework Statement
If limestone (calcium carbonate) and clay (assume aluminum silicate) are mixed together and heated then the result is cement. Cement is a mixture of calcium oxide, carbon dioxide, aluminum oxide, and calcium silicate. These bags can be purchased at any building supplies...
What is the maximum size scale (how many atoms) where the concept of wave function is still useful in chemistry esp. biochemistry? For example. Wave function modelling is easily done in Hydrogen Atom. The interaction Hamiltonian is mostly of the nature E = K + P (Total Energy = Kinetic +...
Homework Statement
If Q = 1.0 1042 for the reaction C(s) + O2(g) → CO2(g) at 25°C, calculate Keq.
dGof (Kj/mol) of...
C(s)=0
O2(g)=0
CO2(g)=-394.36
Homework Equations
dGorxn = -R*T*ln(K)The Attempt at a Solution
-394.36*1000 = -8.314472(298)ln(K)
K=1.3e69
This is the wrong answer. I'm...
lets say there is a pond of 1,000,000 gallons of water.
and the total of 10,000g of chemical is evenly dissolved in the water
Fresh water starts pouring into the pond at the rate of 300 gallons/hour and the pond also releases water at the rate of 300 gallons/hour (hence no change in total...
Hi everyone,
I have been given an assignment with my physics subject and describe in 400 words how electromagnetism can be used to determine the composition of different chemical mixtures
I was hoping someone could lead me to a couple of websites to do my research. I have entered about...
Hi there,
I was just wondering about this point, why do some chemical reactions produce bright light (and even sound) whilst others do not?
For example: in the rapid oxidation of Magnesium in air after given the necessary activation energy, a bright white light is emitted. However, in many...
Homework Statement
Consider a first order decomposition reaction
2P(g) -----> 4Q(g) + R(g) + S(l)
taking place at a temperature T. After 30 minutes from the start of the decomposition in a closed vessel, the total pressure developed is found to be 317 mmHg and after a long time, the...
like this:
1)H2SO4 + Al(OH)3 --> Al2(SO4)3 + H2O
2)Pb2+ + Cl- --> PbCl2
and word equation like this
ethane(C2H6) + Oxygen --> Carbon dioxide + Water vapour
Thq.
Hi,
This may sound like a weird question.
I have extremely painful burning sensation on my lower buttocks and down the back of my upper leg.
I have been to the doctor and he has no answers. Is it possible that I came in contact with some substance that could cause the extreme burning, but...
The more reactive an element, the stronger bonds it forms, because the same energy must be put into that bond to separate them that was put out due to the reaction. Most of the elements we are made of, in pure form, are reactive correct? Carbon and oxygen have very high electronegativities, and...
Homework Statement
If limestone (calcium carbonate) and clay (assume aluminum silicate) are mixed together and heated then the result is cement. Cement is a mixture of calcium oxide, carbon dioxide, aluminum oxide, and calcium silicate. These bags can be purchased at any building supplies...
I am a mechanical engineer who is writing a science fiction novel where a means has been discovered to temporarily reduce the mass of the nucleus of certain 56Fe atoms. When a certain field is applied to the iron, it gets lighter. When the field is removed, the iron regains its original mass...
Homework Statement
Toluene is recovered from a mixture of toluene and nitrogen (containing 52 mol% toluene) by cooling the mixture at constant pressure of 1.2 bar to condense out some of the toluene. If the flow rate of the mixture into the condenser is 179 kmol h-1, determine the flowrate of...
Okay, so I just got done with my fall term classes, and my grades aren't the best. I was wondering two things, one, should I continue? Everyone seems to give me the easy "of course you can do it" spiel, while that is good and dandy, it never tells me anything. I don't know if I really can do it...
Hello. I am currently a physics major attending a university where there is no true engineering degree. I was wondering if one who is pursuing a degree in physics would even have a chance of getting into a program involved with chemical engineering. To me, it seems the further along, physics and...
cabbage chemical composition?
Does anyone know what the chemical composition of cabbage is? I've looked all over the internet and can't find ANY information on this.
I plan to take Engineering as a second degree since I haven't had much luck with my BSc. I'm considering Biomedical (somewhat high paid but jobs are seem to be rare), Chemical (twice as many employed and slightly higher pay) or Mechanical Engineering (highest number employed by a long shot). I...
Homework Statement
12.8 gr of O Flowed over 100 gr hot Al.
and i got this reactions equation: 4Al(s)+3O2(g)--->2Al2O3(g)
a)how many gr Aluminum oxide Al203 Created through a chemical process ?
i know i need to find the number of moles of oxygen which flowed. and the number of...
Hey guys, I am from a Canadian university and have just recently took the GRE (1480 for verbal+quant).
I am thinking of applying for graduate studies in the United States, preferably tier 1 schools such as Princeton, MIT etc.. However, after doing some online research it seems that schools...
I'm looking to do experimental, hands on research on chemical reactor design. Some possibly areas of interest include multiphase catalysis, interface chemistry in fluids and gas liquefaction. I'd like to avoid semiconductors and materials as my background in this area is minimal and I do not see...
So, let's say we have an elementary reaction:
2A --> C
The rate of this reaction is (according to IUPAC: http://goldbook.iupac.org/R05156.html)
- \frac{1}{2} \frac{d[A]}{dt} = k [A]^2
If we integrate this we get a certain integrated rate law (second order)
However, if we multiply all of...
Hey everyone. I hope someone can help. I'm off on this by several factors so I'm wondering what I may be inferring incorrectly.
Homework Statement
Express the chemical potential of an ideal gas in termps of T and V:
\mu = c_{P}T - c_{V}T\ln T - RT\ln V - s_{0}T + const
Homework...
Homework Statement
Knowing some gas entropy
S= Nk_{B}[ln(\frac{V}{N})+\frac{3}{2}ln(\frac{mU}{3\pi\hbar^2N})+\frac{5}{2}] calculate chemical potential.
Homework Equations
\mu = -T(\frac{\partial S}{\partial N})
The Attempt at a Solution
I multiply all the terms by themselvs...
Homework Statement
In a lab we are adding ascorbic acid (C6H8O6) to iron(III) to reduce it to iron(II). I need to come up with a chemical equation showing this. I do not know how to come up with products of the reaction besides iron(II).
2. The attempt at a solution
Fe(3+) + C6H8O6 => Fe(2+) + ?
I'm still deciding between these two majors. I have some interests in chemistry but I don't want to stuck with mundane mixing chemicals in a lab all day. I like MAE because I prefer hands on work (but I might hate it when I'm older) and I like to build and fix things with my hands. I guess I...
Hi,
I'm almost finished my BSc degree in Chemistry in the UK and I'd like to move into Chemical Engineering.
My options are:
MSc Process Engineering;
PhD Chemical Engineering;
BEng in Chemical Engineering at the Open University.
Which route do you guys think is best?
Are there...
This at first may sound like a question based in chemistry, but I feel it is more of a particle physics question.
When a chemical reaction occurs, it can be exothermic or endothermic. It is my understanding that if bonds are formed, energy is released, and when bonds are broken, energy is...
Chemical potential of a substance i in an ideal solution is given by:
\mu_i = \mu_i^0 + RT \log x_i
(where \mu_i^0 is a chemical potential of pure substance i and
x_i is mole fraction of i)
In nonideal solution x_i has to be exchanged with activity coefficient a_i :
\mu_i = \mu_i^0 +...
In order to understand some areas of chemistry I have gotten interested in, I believe it in my best interest to learn reaction equations. Like every other reality situation, there are problems. For one, my school doesn't have the ability to teach me this, secondly, online ones for me are harder...
Is anyone familiar with any chemical reactions that release both oxygen and carbon dioxide gas as products?
Or any reactions where oxygen and carbon dioxide are both reactants?
Thanks.
There are two ways to form these: through Covalent and Ionic bonding, correct? But I have always wondered something about Ionic bonding, if two atoms are attracted to each other due to opposite charges, shouldn't they be close enough to make the electrons be attracted into the opposite atom and...
Homework Statement
A skateboarder with his board can be modeled as a particle of mass 79 kg, located at his center of mass (which we will study in a later chapter). As shown in the figure below, the skateboarder starts from rest in a crouching position at one lip of a half-pipe (point circle...
hi,
DNA and RNA seem to be very peculiar molecular structures that are able to replicate themselves, and they are unique regarding this point, right?. But which chemical "magical" phenomena is responsible for this ability to reproduce?
I know that chemical reactions can emit light and heat, and these are part of the electromagnetic spectrum. But are there any chemical reactions that can directly produce electromagnetic emissions in the radio part of the spectrum?
Homework Statement
A mole of ideal gas with molar heat capacity cv = 3/2 R is initially at 298 K and 10 L and expands (with a constant temperature environment at 298K) in a final volume of 20 L in two ways
a) isothermal and reversible
b) isothermal for a fixed external pressure 0.5 atm...
I have a problem in which It asks to find the equilibrium concentrations but it only give the value of the equilibrium constant and the chemical equation. Is this even possible to solve or does it not have enough information?
Here is the problem
Determine the equilibrium concentrations...
Hello,
As mentioned in my title, I am currrently a freshman studying Chemical Engineering. I chose chemical engineering because I am a thinker, someone who wishes to attempt to solve some of the world's most critical problems through the use of my acquired knowledge in engineering and...
Why some of the chemical reactions are slow? Is it directly proportional to the size and shape of the molecules - since the complex shape makes 2 molecules less probable coming in contact with the appropriate alignment for the chemical reaction to happen?
I'm trying to find an answer within...
Homework Statement
Our chemistry teacher just learned about chemical kinetics. I've been working with the calculus teacher to find out how to determine instantaneous rates exactly. We don't have any equation. Could someone explain this please?
Homework Equations
The Attempt at a...
So I have anida about wanting to major in chemical engineering but I am afraid I might be going into something that I might be underestimating. Can anyone with experience in this field let me know how it is interest wise, because I already know its a lot of work but i want to know if you think...
I had interest in Chemical Engineering since 9th grade. But now when I'm in 12th, Mechanical engineering gained my interest. When I looked at the subjects taught in these branches, some were out of my interest. Now every other branch (aerospace, material science etc) I see, I don't like all...
Hey all.
This really has more to do with uoft. I noticed that the grad program in ChE at UToronto has fewer course requirements, and fewer course options than the other main engineering specializations. I was wondering why that was so.
In contrast, I noticed that McGill's grad ChE program...
In the explicitly-unsolvable Hamiltonian for a chemical system, approximations are made to solve the energy of the system. In particular we see CNDO (ZDO), INDO and MNDO theories.
CNDO - complete neglect of differential overlap; two-center electron integrals are zero.
INDO - intermediate...
Homework Statement
A saturated solution of iodine in water contains 0.330g of I2/L. More than this can dissolve in a KI solution because of the following equilibrium-
I2(aq) +I-(aq) ------> I3- (aq) where 2 and 3 are subscripts and - is negative charge
A 0.1M KI solution actually...