A Sulphur Cycle

A Sulphur Cycle
In the cycle shown below there are three separate chemical reactions represented:

• Reaction 1 : Sulphur powder is heated strongly with iron filings in a test tube. After a while the contents of the tube will glow and iron II sulphide is formed.
   
• Reaction 2 : Once the iron II sulphide has cooled down dilute hydrochloric acid is added to it. This is done in a fume cupboard since one of the products, hydrogen sulphide gas, has a pungent odour similar to bad eggs. The hydrogen sulphide gas is collected in a gas jar.
   
• Reaction 3: Oxygen gas is mixed with the hydrogen sulphide gas. A lighted match will ignite these two gases. The products of this reaction are water and powdered sulphur.

The element sulphur is found in volcanic areas. It forms yellow deposits around the crater of a volcano.

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main Chemical reactions

Chemical Names

In most cases the name of a chemical tells you precisely which elements are present.

When non-metal atoms are combined with metals their name changes slightly in the name of the compound.

For example, calcium combined with oxygen will give calcium oxide. Whenever you come across a compound where the name finishes with -ide you know that this is, in fact, a combined non-metal atom.

Image	Name
	sodium chloride
	calcium oxide
	iron II sulphide

Some chemical names are more difficult to understand. The names of these chemicals need to be learned and remembered!

Image	Name	Notes
	ammonia gas	Made from nitrogen and hydrogen (Ratio 1:3)
	nitric acid	Hydrogen combined with a nitrate radical (Ratio 1:1)
	water	Its correct chemical name is hydrogen oxide! Atoms are re-arranged during a chemical reaction, they are not changed by the reaction. A chemical reaction is shown like this: .... reactant(s) product(s)   The arrow represents the reaction taking place.   The reaction shown below represents the element carbon burning in air. It combines with the oxygen gas in the air to make carbon dioxide gas. + HEAT One atom of carbon (4 bonding arms) reacts with one molecule of oxygen gas) The carbon and oxygen gas need to be heated together for this reaction to proceed. During the reaction the two oxygen atoms were separated and then joined to the carbon atom. In the next example nitrogen gas reacted with hydrogen gas to form ammonia gas.     +     HEAT One molecule of nitrogen gas reacts with three molecules of hydrogen gas. These gases need to be heated together for the reaction to proceed. The reaction produces two molecules of ammonia gas. + HEAT     +     HEAT "Matter can neither be created nor destroyed by chemical means" This is a really important rule to remember when you are making chemical equations. You must always make sure that you have the same number of each type of atom on either side of the chemical equation. You cannot lose or gain any atoms! Take another look at the two equations above: In the first equation you will find one carbon atom and two oxygen atoms on either side of the reaction arrow. In the second equation there are two nitrogen atoms and six hydrogen atoms on the reactants' side of the equation. There are the same numbers on the products' side. Atoms have neither been created or destroyed, they have simply been rearranged to make different molecules. Chemists find the identity of the products of a reaction by experimentation and observation. Study the reaction below: ..... In this reaction hydrogen sulphide gas is burnt in oxygen gas. The products of this reaction are sulphur and water. If hydrogen sulphide gas and oxygen gas are mixed in a gas jar and a burning match or taper is placed near the mouth of the gas jar. A bright, blue flame can be seen that moves down the gas jar. When the reaction is finished you can see a yellow powder on the inside of the gas jar as well as condensation. This yellow powder is the element sulphur. The arrow in the equation tells you that a solid has been made during the reaction. The condensation can be proved to be water by testing with cobalt II chloride paper which turns from blue to pink only in the presence of water. The equation below shows what happens when chalk (calcium carbonate) is heated ..... This reaction is an example of chemical decomposition by heat. The two products are calcium oxide and carbon dioxide gas. The gas can be proved to be carbon dioxide by bubbling it through lime water. Lime water is a specific test for carbon dioxide gas. No other gas will make the lime water turn "cloudy" or "milky". Most metals will react with dilute acids to give a salt and hydrogen gas. Reaction 1 Metal + acid salt + Hydrogen gas Reaction 2 In these reactions the metal replaces the hydrogen. Hydrogen gas is liberated (this is shown by the arrow pointing upwards). The other product is a salt which is formed from the chemical bonding of a metal with a non-metal component. You will notice that the type of salt produced depends on the acid used. Can you identify the reactants and the products shown in the equations above? Note: Dilute acid will have no effect on copper. Copper is not reactive enough to replace the hydrogen in this type of reaction. Sodium and potassium are far too reactive to use safely in the laboratory as the metal reactant.

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Angular Mechanics

Angular mechanics is a branch of mechanics. Angular mechanics involves the study of motion of a body in a rotational or a circular way. The angular momentum and torque are the most important and responsible part for angular mechanics. When the force is applied to a body that causes it to rotate then it creates torque. Similar to force, torque also acts to angularly accelerate a spinning object. The equation for torque (expressed as Γ here) looks very much like force in a linear motion (F = ma) because the torque is analogous to the force in rotational motion.
Γ = Iα
Instead of mass, we have rotational inertia(mass and inertia are analogous to each other). Instead of linear acceleration, we have angular acceleration(linear acceleration and angular acceleration are analogous to each other).

Now, if a force is applied linearly to make an object move, its torque is defined as:
Γ  = F × r
In angular mechanics, angular momentum, moment of momentum, or rotational momentum is a quantity in a rotational motion is analogous to linear momentum in translation motion. Just as linear momentum is equal o the product of mass and linear velocity, angular momentum is equal to the product of M.I. and angular velocity. It is also a vector quantity.
L = r × p = r × mv,
L =Iw
Where,
r- radius of vector,
P-linear momentum,
m- mass of the body,
v- velocity of a body,
I-moment of inertia,
w-angular velocity
Where there is no net external torque, angular momentum is conserved in a system and its conservation helps explain many diverse phenomena. Let us see one example- the increase in rotational speed of a spinning figure skater as the skater's arms are contracted is a consequence of conservation of angular momentum. The another example is-a very high rotational rates neutron stars. It means, angular momentum conservation has numerous applications in physics and engineering.

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Gravity

An object released from some high above the surface of the earth falls freely with an acceleration. This accelerate motion is due to the force of attraction exerted by the earth on the object. The motion of the moon in a circular orbit around the earth also shows that the earth exerts a force of attraction between the sun and suggest the existence of a force of attraction between the sun and the plant. These observations led Newton  to the conclusion that any two material objects always attract each other. This attraction is called gravity or gravitation and the force of attraction is called the gravitational force.
Newton’s law of gravity or gravitation:
The gravitational force between any two material object is given by Newton’s law of gravitation, which is every particle of matter attraction every other particle of matter with a force which is directly proportional to the product of their masses and inversely proportional to the square of distance between them.
Suppose two particles of masses m₁ to m₂ separated by a distance r them according to Newton’s law of gravitation, these particles attract each other with a force whose magnitude (F) is given by
F::m1m2 / r2
f =
where  G is a constant called constant of gravity.
SI unit of GI is Nm²/kg² its dimensions can be determined
[G] =
=
=  [M ^-1L³ T^-2]
The gravitational force between two particles act along the line joining the two particles and they form an action reaction pair. The force exerted by the first particle on the second particle is exactly equal and opposite to the force exerted by the second particle on the first.
Newton’s law of gravitation holds good for all material object irrespective of their sizes or distance between them. Therefore it is called a universal law and the constant of gravity G1 is called the universal constant its value is 6.673 x 10^-11 Nm²/kg². In order to explain how to masses attract each other even though there is no physical contact between them, the concept of gravitational field is introduced. According to this concept, there exists a gravitational field in the space surrounding and mass. When another mass is brought into this space, it is acted upon by the gravitational force of attraction.

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Motion

Change in the position of an object with respect to time is the motion of an object is the motion of an object. Motion is one of the most important part of branch of physics called mechanics. Everybody on the Earth moves. The movement might be slow or very very slow. If we are standing on earth then earth moves around the Sun and Sun moves around the galaxy. It means that the movement of a body never stops.
To have a motion of an object or to change its motion, the force should be acted on an object. When some Physicists observe that, how an object moves? , they use some basic terms like the speed or velocity with which an object moves, the mass of an object which also affects on motion of object, forces acting on an object, acceleration(rate of change of velocity with respect to time), energy and the work.
Some basic equations related to motion:
v(velocity) = s(displacement)/ t(time)
a(accelaration) = dv(changes in velocity) / dt(changes in time)
F(force) = ma where, m=mass
Types of Motion:

• Uniform motion In this type of motion the direction and the speed of an object are the same and do not change with respect to time. In such case, the object moves in the same direction and travels through equal distance in equal interval of time, however these intervals may be small.  Obviously, when the object is in uniform motion, its instantaneous velocity (it is average velocity as the time-interval t becomes extremely small) is the same everywhere along its path. Also its average velocity is the same as its instantaneous velocity.
  
• Variable motion In this type of motion the direction or speed changes with respect to time. In this displacement of an object varies from instant to instant, either increasing or decreasing.
  
• Periodic motion
  The motion that repeats and always returns to its original initial position is called periodic motion. Periodic motion repeats in equal interval of time. Examples of periodic motion are a rocking chair, a bouncing ball, a vibrating guitar string, a swinging pendulum, and a water wave, the motion of the Earth in its orbit around the sun.
  

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Law Of Motion

There are three laws of motion and they were first compiled by Sir Isaac Newton in his work Philosophiæ Naturalis Principia Mathematica, first published on July 5, 1687^. Newton used these laws to explain and investigate the motion of many physical objects and systems. Newton showed that these laws of motion when combined with his law of universal gravitation, explained Kepler's laws of planetary motion.
Newton's laws are applied only to bodies (objects) which are considered or idealized as a particle, in the sense that the extent of the body is neglected in the evaluation of its motion, i.e.,the object is small when compared to the distances involved in the analysis, or the deformation and rotation of the body is of no importance in the analysis. Therefore, a planet is idealized as a particle for analysis of its orbital motion around a star.
Laws of motion are described as follows:

• First law: Every body remains in its state of rest or uniform motion (constant   velocity) unless it is compelled by an external unbalanced force to change that state. It means that in the absence of a non-zero or the net force the center of a mass of a body either remains at rest, or moves at a constant speed in a straight line.
• Second law: The rate of momentum of a body is directly proportional to the impressed force and takes place in the direction of the force. It means a body of mass m subject to a force F undergoes an acceleration a that has the same direction as the force and a magnitude that is directly proportional to the force and inversely proportional to the mass, i.e., F= ma. Alternatively, the total force applied on a body is same to that of the time derivative of the linear momentum of the body.
• Third law: To every action, there is equal and opposite reaction or the mutual forces of action and reaction between two bodies are equal, opposite and collinear. It means that whenever a first body exerts a force F on a second body, the second body exerts a force   -F on the first body. F and -F are equal in magnitude and opposite in direction. This law is usually referred to as action-reaction law with F called the "action" and -F the "reaction".

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Banking of a Road Surface

Mechanics

Banking of a Road Surface

Moving in a Straight line on a Horizontal Surface

Turning on a Horizontal Surface

The normal reaction, R, has no component acting towards the centre of the circular path. Therefore the required centripetal acceleration is provided by the force of friction, Ff, between the wheel and the road. If the force of friction is not strong enough, the vehicle will skid.

Turning on a Banked Surface

The normal reaction, R, now has a component acting towards the centre of the circular path. If the angle, , is just right, the correct centripetal acceleration can be provided by the horizontal component of the normal reaction. This means that, even if there is very little force of friction the vehicle can still go round the curve with no tendency to skid.

Angle of Banking

The magnitude of the horizontal component of the normal reaction is

This force causes the centripetal acceleration, so, the magnitude of R_H is also given by

equation 1

 So,

equation 2

The vertical forces acting on the vehicle are in equilibrium.

Therefore, considering magnitudes only

Dividing equation 1 by equation 2 gives:

This equation allows us to calculate the angle needed for a vehicle to go round the curve at a given speed, v, without any tendency to skid.

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How Dry Cell Batteries Generate Electricity

written by: Aggeliki K. • edited by: Lamar Stonecypher • updated: 5/20/2011

Normally a dry cell is also referred to as a Zinc-Carbon Leclanche cell. It is an easily portable, compact, and modified form of Leclanche cell capable of producing an EMF of 1.5 V with a very small internal resistance in the order of 0.1 ohm.

• Dry Cell History and Advances

  The first dry cell was invented in the late 19^th century. It used zinc as an anode, manganese dioxide as an “earthode,” and a gelled, moist mixture of ammonium chloride and zinc chloride as electrolyte.
  Later they created a dry cell made up of carbon as a cathode, zinc as an anode, and sal-ammoniac paste as an electrolyte. This type of dry cell is commonly known as a carbon zinc Leclanche cell. Even today, most of the dry cells manufactured are of this kind due to its lower manufacturing cost and its being suitable for all applications requiring intermittent current, such as used in flashlights and transistor receivers.
  These cells have a few drawbacks such as their low energy density and limited lifetime. In later years, a large number of new types of dry cells were developed for new and different applications.
  Modification in Leclanche Cell to become a Dry Cell
  The glass in Leclanche cell is replaced by a zinc container, and the ammonium chloride solution is replaced by a moist sal-ammoniac paste.
  The Dry Cell is a Primary Cell
  

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  The cells from which electric energy is derived by irreversible chemical action are called primary cells. The primary cell is capable of providing an EMF when its constituent’s two electrodes and a suitable electrolyte are assembled together. The three main primary cells namely are the Daniel cell, the Leclanche cell, and the dry cell. None of these cells can be recharged electrically.

• Commercial Dry Cells

  

• How Chemical Energy is converted into Electrical Energy in Cells

  Chemical effect of current
  Conversion of electric energy into chemical energy: the passage of an electric current through a liquid causes chemical changes through a process called electrolysis. Conduction is possible only in liquids wherein charged ions can be dissociated in opposite directions. Such liquids are called electrolytes, and the plates through which current enters and leaves an electrolyte are known as electrodes. The electrode towards which positive ions travel is called the cathode, and the electrode towards which negative ions travel is called the anode. The positive ions are called cations and negative ions are called anions.
  Effect of Chemicals in Batteries
  Conversion of chemical energy into electrical energy: in this case, the reverse process takes place due to the chemical reaction between two electrodes in the presence of an electrolyte and an electric current is produced.
  Faraday’s Laws of Electrolysis
  First law:
  The mass of a substance liberated at an electrode is directly proportional to the charge passing through the electrode.
  Second law:
  The mass of a substance liberated at an electrode by a given amount of charges is proportional to the chemical equivalent of the substance.

• Working of a Dry Cell:

  Parts:
  Anode (Negative Terminal): Zinc
  Cathode (Positive Terminal): Carbon coated with MnO2
  Electrolyte: Mixture of plaster of Paris, Ammonium Chloride and Zinc Chloride
  Dry cells contain a Zinc container which itself acts as a negative electrode. The moist paste is made from a mixture of plaster of Paris, Ammonium Chloride, and Zinc Chloride called sal ammoniac paste. This forms the electrolyte of the cell and takes up the major amount of volume in the battery. Zinc Chloride is hygroscopic in nature and helps to maintain the moistness of the paste. It is wrapped in a canvas sheet.
  

  • Anode reaction: The oxidization of Zinc gives two electrons.

  Zn(solid) → Zn2 + (aqueous) + 2 (e-)
  The carbon rod forms the positive electrode. It is coated with MnO₂ and powdered carbon. The powdered carbon reduces the internal resistance of the cell. The top of the cell contains a layer of sawdust. This acts as the base for the top layer of bitumen used for sealing purposes.
  

  • Cathode reaction:

  2MnO2(solid) + H2(gas)→ Mn2O3(solid) + H2O(liquid)
  

  • Electrolyte reaction: Hydrogen from Ammonium chloride

  2NH4 + (aqueous ) + 2 (e-) → H2(g) + 2NH3(aqueous)
  

  • Overall reaction in dry cell:

  Zn(s) + 2MnO2(s) + 2NH4(+)(aqueous) → Mn2O3(solid) + Zn(NH3)2 (2+)(aqueous) + H2O(liquid)
  
  
  A vent is provided in this layer to allow the gases formed in the chemical reaction to escape. Irrespective of the size of the dry cell, the EMF is 1.5 V because the zinc and carbon rods used as electrodes specified a chemical equivalent. The chemical equivalent changes from metal to metal and, depending on the type of combination used, the EMF differs.
  

• Dry Cell Parts

  

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