SPECIFIC HEAT CAPACITY SECTION CParts:3.1-3.4
Specific Heat Capacity • The specific heat capacity of a substance is the amount of heat requires to increase the temperature of unit mass of a substance by one degree Celsius. • Units- 1) c/J 2) Kg-1 K-1
Heat Capacity • The heat capacity (C) of an object is defined as the heat required to raise its temperature by one degree. • The rise in temperature of a body which is heated, without a change in state depends on : the mass of the body. The nature of the substance of which the body is made. • the formula for heat capacity is C=mc Where C is heat capacity, m is mass and c is the specific heat capacity.
Specific Heat Capacity Formula • Equal quantities in heat supplied to the same mass of a given substance produce the same temperature rise. • The temperature rise for a given quantity of heat supplied depends on the mass of the substance involved. • The same quantity of heat supplied to equal masses if different substances results in different temperature changes, depending on the different specific heat capacities of the materials. heat supplied = mass of substance X SHC X Temperature Rise EH = m (Kg) X c (J Kg-1 K-1 ) X Δθ (K)
Examples • How much energy is needed to heat 100g of water from 100C to 300C? Specific heat capacity of water = 4200J/kg 0C. mass of water = 100g = 0.1kg temperature rise = 30 0C - 10 0C = 20 0C Heat needed = SHC * mass * temperature rise EH = 4200 * 0.1 * 20 joule = 4200 * 2 joule = 8400 J
Determining Specific Heat Capacity • To determine the specific heat capacity of a material be it a liquid or gas two methods can be used: • The Electrical method. • Method of mixtures. • The Electrical method To find the specific heat capacity of a substance using this method would involve the use of a thermometer, water, beaker, electrical heater and a stirring rod. In a determined volume of water , place an electrical heater, turn it on and stir with the rod to keep the heat moving. All the while a thermometer is should be in the water to determine the changes of temperature for the allowed amount of time. The initial temperature of the water and all temperature changes after the electrical heater was turned on must be taken at regular intervals.
The Method of Mixtures When two objects at different temperatures are placed in thermal contact, the hot object losses heat and the cold object gains the heat lost by the hot object. therefore we can say: Heat lost by a hot object = Heat gained by a cold object Method: Hot the water to boiling point, place a rod into it and leave it for a few minutes until the rod is at the same temperature as the water. The rod is then quickly taken out of the first beaker and placed into a second beaker filled with water at room temperature. Stir the water continuously to keep the heat moving. With the use of a thermometer take the changes of temperature at regular intervals until no more change is seen. Formula:Heat gained by substance = Heat lost by other substance m1* c1* Δθ1 = m2* c2* Δθ2
Example • A block of metal of mass 0.8 kg at 100 0C was placed in 0.4 kg of water at 30 0C. The final steady temperature of the mixture was 43.5 0C. What is the specific heat capacity of the metal? Temperature rise of water = (43.5 – 30) 0C = 13.5 0C Temperature drop of the block = (100 – 43.5) 0C = 56.5 0C Heat lost by block = Heat gained by water m1* c1 * Δθ1 = m2* c2* Δθ2 0.8 * c block* 56.5 = 0.4 * 4200 * 13.5 c block = 502 J Kg-1 K-1
PHASES OF MATTER SECTION C Parts: 3.5, 3.6
States of Matter Matter is anything in the universe that has a mass and occupies space. The quantity of matter contained in an object determines its mass. Since materials are made up of small particles of simple substances, the quantity of matter in a material depends on: • The quantity of matter in each individual particle of each simple substance. • The way in which these particles are packed, i.e..whether tightly or loosely packed All matter be it any of the three states consists of atoms. An atom is the smallest unit that can exist. The state of matter depends upon the energy(kinetic energy) the atoms contained within the object has. As a result changing the amount of energy the atoms has, changes the state of the object
There are three states of matter: • Solids • Liquids • Gases Solids Atoms within a solid are tightly packed due to the strong intermolecular forces between them and as it possess very small amounts of kinetic energy. Due to these strong forces the shape of the solid is fixed as the atoms can only vibrate about a point and the volume is definite with very little compression or expansion ability.
Liquids Atoms within a liquid are randomly arranged with small spaces between them. This is so as the intermolecular forces are fairly weak and allows the atoms to move slowly as it posses medium kinetic energy. Due to this weak intermolecular force the shape of the liquid is that of the container it is placed in with the surface always being horizontal, and a definite volume. Liquids can be expanded and compressed slightly
Gases Atoms within a gas are randomly arranged with large spaces between them. The intermolecular forces is very weak and allows rapid movement since it posses a large amount of Kinetic energy. Due to this weak force the volume of the gas is variable meaning that it expands to fill the container and takes the shape of the container. Gases can be easily expanded or compressed.
Credits and Bibliography • Heinemann Physics for CXC – Norman Lambert • Practical Physics for CXC – Gillian Blackman-Herbert • Physics for You – Keith Johnson • ***Mr Ramdath notes • http://en.wikipedia.org/wiki/Heat_capacity#Heat_capacity • http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html#c1 • http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html#c1 Done By: Fadilah Khan 5C