Effect on Melting Point of Ice: Melting of snow and making of ice-cream

The normal melting point of ice is 0°C i.e. at atmospheric pressure. When the pressure is increased, the melting point of ice decreases. like if if we press the ice it starts melting, this property is used by snow skiers, they press the snow to liquify it which act as lubricant.

The melting point also changes with adding impurities. When salt is added to water the melting point decreases below 0°C i.e. depression in freezing point. This property is used in melting of snow, as well as making of ice. How?

During snow fall, when salt is sprayed to snow the melting point decreases. In case of NaCl, the melting point (freezing point) changes to -7°C i.e. ice will start melting at a temperature of -7°C.

If surrounding temperature is -2°C, the snow (pure water) will remain in solid form but if salt is added, then it will melt.

The same principle is used while making ice cream or used for chilling the ice-cream.

the temperature of pure ice (let's say -10°) will increase rapidly to 0°C as less specific heat and it will become constant at 0°C till all the ice melt. So, this can't be used to make ice-cream. But if salt (NaCl) is present, the temperature of ice from -10°C will increase to -7°C at which it will become constant for some time till all the ice melts. So, in this way we can create a suitable temperature for freezing ice-cream.

Cell Potential of a electrochemical cell

Electrochemical cells have inheritance advantage of higher efficiency as compared to conventional source of electricity generation. In electro-chemical cell the chemical reaction is split in two separate half reactions known as oxidation half reaction and reduction half reaction.
There are two electrodes known as anode and cathode, at anode oxidation takes place while at cathode reduction takes place. During oxidation, electrons are released at the electrode and makes it negative charge while in reduction electrons are used, therefore cathode is positive charge.
As the two reactions are opposite, the potential of the cell is addition of potential of two electrode:
Ecell = E_anode (oxidation potential) + E_cathode (reduction potential)
as oxidation potential = -reduction potential
 Ecell = -E_anode (reduction potential) + E_cathode (reduction potential)
               E_cathode (reduction potential) - E_anode (reduction potential)

Properties of solids for size reduction

We should understand the properties which are useful to find the size reduction method of solids. these properties tell about what type of reduction mechanism and equipment is suitable and how much power is required.
1. Hardness: resistance to identation or scratching. the hardest mineral is diamond. hardness is usually expressed in terms of Moh's scale. Minerals with a Moh's hardness of 4 or less are classed as soft; others are considered hard. for hard materials, crushers are used like jaw, gyratory or disk, while for soft material like coal, hammer mills or toothed rolls are used.
2. Brittleness: ease with which a substance may be broken by impact.

Simulation using Excel

Excel can be used to solve simulation problems. like gravity flow tank
write the mass balance and equation of motion as:

with the dimensions of tanks and pipe and initial conditions, the variables are flow rate f (or velocity v) and height h, and we have two equations to solve.
steps to solve:
1. with the initial conditions find the derivatives dh/dt and dv/dt
2. calculate the new values of h and v by using the definition of derivative i.e.
v2 = v1 + dt*dv/dt
h2 = h1+dt*dh/dt
3. with new values calculate the derivatives
4. caluclate the new values of the variables
5. repeat till  the values we get converged values.

Partial and Total Condenser

In Distillation the vapor from the top are condensed and re-fluxed it to the top tray to have the contact between liquid (low temperature) and vapor (comparatively higher temperature). The product from the top can be taken as liquid or vapor:

if the product is liquid, the condenser is called total condenser;

if the product is vapor then it is partial condenser.

Total condenser: the vapor phase composition is same as the liquid phase composition as all the vapors are condensed, the amount of the components is same. 

Partial condenser: the vapor and liquid are in equilibrium. this will act as an additional tray for the separation. the vapor will be enrich in more volatile component

Intensive and extensive properties

Intensive properties are independent of quantity. If we add moles to a closed vessel then pressure will increase. then is pressure an extensive property?

if we take one mole from the system, the property value of 1 mole and that of remaining moles is the same then it is intensive property. Like pressure inside an open bottle placed in a room is the same as the pressure in the whole room.

Use of Hydraulic Power in bicycle or hand lifting machine

Hydraulic power increases the force that we apply. If we apply 1 N force on 1cm2 then it will be equal to 10 N force acting on 10 cm2. can we use this in bicycle, automobile to increase the mileage or hand lifting machine.