MYP+11.1+Heat+Capacity

**IB MYP Thermal Physics**
Go back to Sec 3 and 4 Contents Page

=Thermal Properties of Matter=

The amount of energy stored in the bonds depends on the force between the particles and how far apart the particles are.

 * ======If the temperature of a substance rises, it is due to an increase in the average __ kinetic __ energy of its particles only.======

**Q = mc(ΔΘ) = C(ΔΘ)**
Question A The total thermal capacity of a calorimeter, the heater, the stirrer and the thermometer is 107 J K -1. The mass of the liquid in the calorimeter is 0.241 kg. The whole set-up is at room temperature when the heater coil is turned on with a potential difference of 12.2 V supplying a current of 3.40A. The initial rate of rise of temperature is found to be 3.7 x 10 -2 Ks -1.
 * 1. Calculate the power supplied by the heater.**
 * 2. Calculate the specific heat capacity of the liquid.**

Question B An electric heating coil supplies 50 W of power to a metal block of mass 0.60 kg and raise the temperature of the block from 20 o C to 45 o C in 90 s.
 * Calculate the specific heat capacity of the metal.** What assumption did you make to arrive at your answer?

Question C The heat capacity of a block of metal is 600 J o C -1. (a) What is the heat required to raise its temperature? (i) by 5 o C (ii) from 30 o C to 50 o C (b) If the initial temperature of the metal block is 100 o C, what is its final temperature after it loses 2400J of heat?

Question D Calculate the total heat required to raise the temperature of 2.0 kg of water in an aluminium kettle of mass 0.50 kg from 30 o C to 100 o C. [Specific heat capacity of water and aluminium is 4200 J kg -1 o C -1 and 880 J kg -1 o C -1 respectively.]

Question E A copper block of mass 400g is heated using a Bunsen burner. It is then transferred into 200 g of water initially at 30 o C. The final temperature of the mixture is 50 o C. What is the temperature of the copper block?

Question F A 50 W immersion heater is used to heat a beaker containing 300g of ethanol. The mass of the beaker is 60g and the initial temperature of the ethanol is 30 oC. What is the final temperature of the ethanol after the immersion heater has been switched on for 10 minutes? [Specific heat capacity of ethanol and glass is 2500 J kg -1 o C -1 and 650 J kg -1 o C -1 respectively.]

Specific Heat Capacity

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The specific heat of a substance is an important physical property because it tells us the suitability of a given substance for a specific purpose. Aluminium vessels are used in cooking because aluminium is a light metal. Hence, for a given volume, its thermal capacity will be less than that of vessels made of steel of same volume.======

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The high specific heat of water explains why land close to a large pond of water is likely to have a milder climate than land without a pond close by. Because of high specific heat, water on the land gets heated slowly. Land near the pond also gets heated slowly. For the same amount of heat, dry land gets heated quickly to a much higher temperature. Soil is a poor conductor, prevents the heat from going deep into the ground. Hence, the heat causes a quick rise in temperature on dry land. For same reasons, land areas far from water-cool off much faster than land near large bodies of water.======

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Latent Heat
Latent heat is the __ energy __ released or __ absorbed __ during a change of state. There is no __ temperature __ change as all the thermal energy is used to make (in freezing) or break (in boiling) the__ intermolecular __ bonds; Latent heat of fusion, Latent heat of vaporisation.


 * ===Latent heat of fusion=== ||

Latent heat of fusion [L f ] of a solid is the amount of thermal energy required to change it from solid to liquid state, or vice versa, without a change in __ temperature __. The unit for L f is joule (J). A solid with more mass will require more __ thermal energy __ to melt it. It has more latent heat.

The specific latent heat of fusion //l// f of a solid is the amount of thermal energy required to change 1 kg of the solid to liquid, or vice versa, without any change in temperature. The unit for //l// f is joule per kilogram (J kg -1 ).

Lf = //l// f x m
L f  is the latent heat of fusion.  //l// f is the specific latent heat of fusion. m is the mass of solid.

A heater which supplies thermal energy at a constant rate of 1000 W is completely immersed in a 3.00 kg block of ice at 0 o C. The block of ice takes 1020 s to melt completely. Calculate a value for the specific latent heat of fusion of ice. What assumption did you make in your calculation?
 * Question A **

An ice-cream has a mass of 150g. If the specific latent heat of fusion of ice is 340,000 J or 340 kJ, find the thermal energy required to melt the ice-cream.
 * Question B**


 * ===Latent heat of vaporisation=== ||

Latent heat of vaporisation [L v ] of a substance is the amount of thermal energy required to change it from liquid to vapour state, or vice versa, without a change in __ temperature __. The unit for L v is joule (J). The specific latent heat of vaporisation //l// v of a substance is the amount of thermal energy required to change 1 kg of the liquid to vapour, or vice versa, without any change in temperature. The unit for //l// v is joule per kilogram (J kg -1 ).

==L v  = //l// v x m ==

L v  is the latent heat of vaporisation. <span style="font-family: 'Trebuchet MS',Helvetica,sans-serif;"> //l// v is the specific latent heat of vaporisation. m is the mass of liquid.

**Question A** A jet of steam at 100 o C is directed for a short time at a large block of ice at 0 o C. Some of the steam forms 0.40 kg of water and some ice is melted. The condensed steam forms 0.40 kg of water at 0 o C. 1. Calculate the thermal energy given out by this mass of steam in changing to water at 100 o C. 2. Calculate the thermal energy given out by this water as it cools to the temperature of the ice. (Specific latent heat of vaporisation of water = 2200 kJ kg -1, Specific heat capacity of water = 4.2 kJ kg -1 K -1 )

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[|Heating curve of water] from duckingsciencebombs.wordpress.com