Use the phase diagram of water to explain?

why ice at the bottom of a glacier can melt when the rest of the glacier which is the same temperature remains solid.

joeyeehu...

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You are right.
If you look at the phase diagram of water, you will notice that the melting point curve slants to the left. It has a negative gradient. This means that the melting point of water decreases as the pressure is increase. At the bottom of glacier, it experiences a greater pressure, hence its melting point decreases. This means that it will only become ice at a lower temperature. At that temperature, the liquid water is more stable, hence it melts.In your phase diagram, you just draw a vertical line upward(increase in pressure) from the melting point curve and you will be in the liquid region of the phase diagram.

Why is it that only a few drops of indicators are used for an acid-base titration?

Is it something to do with the indicator being able to change the pH of the solution itself if too much is added, or perhaps it cannot accurately tell the end point once too much is added?

joeyeehu...

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Indicator itself is a weak acid or a weak base.

Adding too much of indicator will influence the pH of the solution and hence will not be able to change colour at the end point.

That's why only two drops of indicator are usually used.

What are the approximate bond angles?

CCl4

BCL3

CF4

SF2

NI3

CCl2F2

joeyeehu...

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CCl4, CF4 and CCl2F2 come under the same category. The carbon atom is surrounded by four electron pairs and all the electron pairs are the bonding pairs. Therefore they have the tetrahedral shapes with the approximate bond angles of 109.5 degree.

For NI3, the nitrogen atom is surrounded by four electron pairs but there are three bonding pairs and one lone pair. Therefore, the shape of NI3 is trigonal pyramidal. The repulsive force between lone pair - bond pair is greater than the bond pair - bond pair. Hence the bond angle is slightly smaller than 109.5. The approximate bond angle is about 107 degree.

For SF2, the sulphur atom is surrounded by four electron pairs but there are two bonding pairs and two lone pairs. Therefore, the shape of SF2 is ' V ' . The repulsive force between lone pair - lone pair is greater than between the lone pair - bond pair . Hence the bond angle is even smaller than 107. The approximate bond angle is about 104.5 degree.

For BCl3, the boron atom is surrounded by three electron pairs and the three electron pairs are all bonding pairs. Therefore the shape of BCl3 is trigonal planar and the bond angle is 120 degree.

Order of reaction question?

for the reaction 2NOBr(g)----->2NO(g) +Br2(g), the rate of equation is -d[NOBr]/dt =k[NOBr]^2. the overall rate reaction =


how do you go about doing this question? my answer appears to be wrong....I have a choice of 1,-1,2 and 0.5

joeyeehu...

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When you are given a rate equation, you can easily tell the overall order of reaction.

lets the rate equation be
rate = k [X] [Y]^2 [Z]^3

We can conclude that:
1) The order of reaction with respect to (wrt) X is 1( because the equation shows that the concentration of X is raised to power 1)
2) The order of reaction wrt Y is 2.
3) The order of reaction wrt Z is 3

4) The overall order of reaction is 1 + 2 + 3 = 6

So, the answer to your question is 2.

Help with this tough AP Chemistry Problem?

N2(g)  +  2O2(g)  <-->  N2O4(g)

If the value of the equilibrium constant with regard to pressure (Kp) is found to be 1.5 at 15°C, what is the value of the eqilibrium constant with regard to concentration?
(R = 0.0821 L•atm/(mol•K))



a. 8.4 x 102
b. 2.3
c. 9.4 x 107
d. 2.7 x 10–3

joeyeehu...

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Assume that the unit of Kp is atm-2.

Kp = Kc ( RT) ^ -2

Substitute the values into the equation, (a) is the answer.

T= 15 + 273 K
-2 is the number of moles of the products minus the number of moles of ractants. ( 1 - 3 = -2 )

AS CHEMISTRY HELP!!!!!!!!!!!!!!!?

1) In order to obtain a mass spectrum of a gaseous sample of chromium, the sample must first be ionised.

(i) give to reasons why it is necessary to ionise the cromium in the sample.

(ii) State what is adjusted so that each of the isotopes of chromium can be detected in turn.

(iii) Explain how the adjustment given in part (ii) enables the isotopes of chromium to be separated.

joeyeehu...

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1) The chromium atom must be ionised to form Cr+ so that it can be accelerated towards the negative plates and deflected by the magnetic field onto the detector so that a mass spectrum can be produced.

Positive ion will be attracted towards the negatively charged plates and charged ion can be deflected by the magnetic field.

2) The strength of the magnetic field is adjusted.

3)The angle of deflection of ion is proportional to the charge of ion and is inversely proportional to the mass of ion. That means lighter ion is deflected more compared to heavier ion.

By having a lower strength of magnetic field, the lighter ion is directed onto the detector first. As the strength of the magnetic field is increased, the heavier ion in turn is directed onto the detector until all the ions with different masses are detected and a mass spectrum is produced.

Rate Constant Chemistry?

What is the rate constant for a second order reaction when the initial [A] = 0.20M, the initial [B] = 0.86M and the initial rate = 0.0900 M/s?

joeyeehu...

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For the second order reaction, the rate equation is

rate = k [A] [B]
substitute the values given,

0.09 = k( 0.2) ( 0.86 )

solve for k.

n which do you overcome dipole-dipole forces?

In which do you overcome dipole-dipole forces?

1) Decomposing water into H2 and O2.

2) Evaporating PCl3.

3) Subliming solid C10H8.

4) Melting propane.

joeyeehu...

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2) Evaporating PCl3.

Evaporating PCl3 will make sure that the PCl3 molecules are far apart. This will make the dipole-dipole forces insignificant.

Dipole-dipole forces only take place if the molecules are polar. PCl3 is polar but the others are non-polar

What is the overall order of the reaction and the order with respect to [O3]?

Consider the reaction

2O3(g)    ->    3O2(g)

rate =  k[O3]^2 [O2]^−1 .
What is the overall order of the reaction and the order with respect to [O3]?

there are answer choices:
1. −1 and 3
2. 0 and 1
3. 1 and 2
4. 3 and 2
5. 2 and 2

Please explain how to do it too, I need to know how to work it out.

joeyeehu...

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When you are given a rate equation, let say

rate = k [A]^x [B]^y [C]^z

we can say that the order of reaction with respect to (wrt) A is x.
The order of reaction wrt B is y and
the order of reaction wrt C is z.

The overall order of reaction is x + y + z

So, the answer to your question is obvious.
It is 3) 1 and 2

overall order is 2 + (-1) = 1

What is the relationship between structure and Rf value?

joeyeehu...

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Rf stands for the retention factor in chromatography. It is a measure of how strongly the substituents are attached (adsorp) to the stationary phase. The stronger the adsorption, the lower is the Rf value.

By the way, Rf can be calculated by dividing the distance covered by the substituent with distance covered by the mobile phase.

A bulky structure ( branched isomer) has a weaker bond compared to a straight chained isomer. This is because the area of contact betweeen molecules is less compared to the straight chained isomer. ( van der Waal forces) Hence it moves faster and have a higher Rf value

If the substituent can form hydrogen bond with the stationary phase, then its Rf value will be lower as the strong hydrogen bond will cause the substituent to move at a slower pace along the stationary column.

How do I determine which molecules are polar?

I am given CCl4, CH4, H3C-CH2-CH2-CH2-CH2- CH3, H2O, CO2, and O2

joeyeehu...

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To determine the polarity of a molecule, you need to know two things.

a) Determine whether the bonds are polar?
b) Determine whether the molecule is symmetrical.(shapea)

A polar molecule must have polar bond and the molecule must be assymmetrical (not symmetrical).

A polar bond is formed if the atoms are of different electronegativities.

a) CCl4 -----> polar bond but symmetrical---> non polar
b) CH4 -----> polar bond but symmetrical---> non polar
c) same as above
d) H2O -----> polar bond and assymmetrical (V-shaped)--> polar molecule
e) CO2 -----> polar bond but linear in shape (symmetrical) ----> non polar
f) O2 --------> non polar bond-----------------------> non polar

What is the rate law of the following mechanism:?

E  +  S   <- ->   ES       (fast)
   ES         ->  E + P    (slow)

E is enzyme, S is substrate, P is product.

joeyeehu...

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let the rate constant of the forward reaction be k1;
let the rate constant of the backward reaction be k2;
let the rate constant of the forward reaction of the second eq be k3

For the first reversible equation:(fast)
forward reaction: rate = k1 [E][S]
backward reaction: rate = k2 [ES]

At equilibrium, rate of forward reaction = rate of backward reaction
k1[E][S] =k2[ES]

[ES] = { k1[E][S] } / k2 ......................(1)

For the slow reaction:

rate = k3 [ES]...................................(2)

Substitute (1) into (2)

rate = (k3) { k1[E][S] } / k2

rate = k [E] [S] ; where k = (k3)(k1) / k2

Will C2H5F or C2H5OH have the higher boiling point? why?

This is a question about Chemistry. London Forces, Hydrogen Bonding and Dipole-Dipole.

joeyeehu...

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C2H5OH would have a higher boiling point because it can form hydrogen bonds between its molecules. So, more energy is needed to break the strong hydrogen bond.

In order to form hydrogen bond, the hydrogen atom must directly attached to a very electronegative atom such as N, O or F.
In C2H5F, all the H are attached to the carbon atom whereas in C2H5OH, one of the hydrogen atom is attached to the oxygen atom.

Further more, the size of C2H5OH is bigger than C2H5F. The bigger the size, the stronger is the London Force.

Chemistry A level equilibria problem?

On heating, X decomposes reversibly according to the equation:

X (g) ↔ Y (g) + Z (g)

This reaction was allowed to reach equilibrium.

(a) When 1.00 moles of X was heated at 200'C in a container of volume 25.0dm3, the equilibrium mixture was found to contain 0.200 mole of Y. Calculate the value of Kc at this temperature.

if anyone can help, much appreciated :)

joeyeehu...

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........................ .X (g)   ↔   Y (g) + Z (g)

initially ..............1.00..........0...........0
change...............0.2...........0.2.....…0.2

At equilibrium .....0.8..........0.2.........0.2

concentration.......0.8/25.. 0.2/25... 0.2/25

Kc = [Y] [Z] / [X]

......= {(0.2/25) (0.2/25)} / (0.8 /25)
......= 2.0 x 10^-3

Why is the oxide of Si solid while the oxide of C is gas at room temperature?

joeyeehu...

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The oxide of carbon, CO2 and CO exist as simple melecular structure. The intermolecular forces of attraction between the molecules is the weak van der Waals force. Hence they have low melting and boiling points and at room temperature and atmospheric pressure , they exist as gas molecules.

The oxide of Si, that is SiO2 exist as giant covalent structure. The Si atom and oxygen are bonded together by strong covalent bond tetrahedrally forming a very big molecules. A large amount of energy is needed to break the covalent bonds as well as the giant structure.

That's why it has a very high melting and boiling points. Hence, it exists as solid at room temperature.

pH chemistry question help!?

Could someone help with this question? And explain why

A known volume )1mL) of a 0.100M NaOH solution was diluted to a total volume of 10.0mL (Solution A). Next 1.00mL of this solution was diluted to a total volume of 50.mL (Solution B) What is the pH of solution B?

joeyeehu...

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Using M1V1 = M2V2,
0.1 x 1 = M2 x 10
M2 = 0.01M (solution A)

Repeat the same process,
0.01 x 1 = M3 x 50
M3 = 0.0002 M (solution B)

Since NaOH is a strong alkali
[OH-] = 0.0002M
 pOH = -log [OH-]
         = 3.70

pH = 14 - 3.70 = 10.30

Resolved Question

Chemistry question- general organic?
Explanation of inductive effect and how it effects acidic behaviour??

by joeyeehu...
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Inductive effect can be divided into two types, positive inductive and negative inductive.A group or atom is said to have a positive inductive effect if it tends to push away electrons away from them(electron donating group). I will increase the electron charge density of its neighbour. Example of such group is the alkyl group ( CH3, C2H5 ).Electron withdrawing group will attract the electrons toward itself (negative inductive effect), ex. F, Cl, NO2. They will reduce the electron charge density of the O--H bond. This will weaken the O--H bond and the molecule is able to donate the H+ more easily. It increases acidic behaviour. ( acid is a proton(H+) donor )

Why does oxygen is a gas but sulphur a solid?

joeyeehu...

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The melting and boiling points of a substance will determine whether it will exist as solid, liquiq or gas at room temperature.

A substance with high melting and boiling points usually exists as solid at room temperature.

Oxygen exists as a diatomic molecules whereas sulphur exists as S6.
Both oxygen(O2) and sulphur(S6) are non polar molecules. Between the molecules, there are intermolecular forces of attraction(IMFOA). This IMFOA is called van der Waals forces. The strength of van der Waals forces depends on the size of the molecules. Since S6 molecules is larger than O2 molecules, the v.d.W forces between the S6 molecules is stronger than that between the O2 molecules, the melting point of sulphur is higher than that of O2. Hence sulphur exists as solid and O2 exists as gas( it has a very low melting and boiling point)