Chapter 12

 Celsius and Fahrenheit scales are the two most commonly used scales.  They were both designed with reference to the freezing point and boiling point of water  Positions were marked on a thermometer for these two temperatures and graduates were made in equal increments  Celsius is used more often around the world

 The size of a Celsius degree is larger than that of a Fahrenheit degree by a factor of 9/5.

 Introduced by William Thompson (Lord Kelvin)  Not expressed with the word “degrees”  SI base unit for temperature  Based on the concept of absolute zero.absolute zero

 Measure changes in thermometric properties  Several types exist including  Thermocouple  Electric resistance thermometers  Thermograph or thermogram  Type needed depends on goal of research and necessary procedure  Here, we will use a regular mercury or alcohol thermometer.

 Linear Expansion is the increase in one dimension of a solid due to an increase in temperature.  The length (L o ) of an object changes by an amount (∆L) when its temperature changes by an amount (∆T). α is the coefficient of linear expansion. α is a constant. This constant is a numerical description of the degree of thermal expansion solids will undergo when heated. Values can be obtained in your text (p.365) or online.

 Thermal Stress – buildings using steel supports must account for expansion in order to prevent “buckling” of steel beams  Bimetallic Strip – used in coffee pots, thermostats, etc.  Expansion of Holes – A hole in a piece of solid material expands when heated and contracts when cooled, just as if it were filled with the material that surrounds it.  Holes with larger coefficients of linear expansion expand more than those in materials with smaller coefficients.

 It makes sense that if the length of an object expands when heated, the volume would too.  The volume (V 0 ) of an object changes by an amount (∆V) when its temperature changes by an amount (∆T). β is the coefficient of volume expansion.

 If water at 0°C is heated, its volume decreases until the temperature reaches 4°C.  Above 4°C, water behaves normally and volume will increase as temperature increases.  The density of water is greatest at 4°C. Click here to find out why volume of ice is greater than volume of water.

 Heat is energy that flows from a higher- temperature object to a lower-temperature object because of the difference in temperatures.  SI Unit: joule (J)  Substances DO NOT contain heat. Instead, they contain internal kinetic energy due to the motion of their molecules or atoms.  Heat is only used to describe the energy in transit from one substance to another.

 The heat (Q) that must be supplied or removed to change the temperature of a substance of mass (m) by an amount (∆T) is c is the specific heat capacity of the substance. Basically, this constant describes how quickly or slowly a substance will change temperature 1 kcal = 4186 joules 1 cal = joules

 Remember: In a closed system, energy is neither created nor destroyed.  A calorimeter is a container used to determine the specific heat capacity of a substance.  In following the law of conservation of energy we can say that heat lost = heat gained.

 During phase changes, addition or removal of heat will not cause temperature changes.  Once the phase change is complete, the addition or removal of heat will cause a change in temperature.

 The heat (Q) that must be supplied or removed to change the phase of a mass (m) of a substance is L is the latent heat of the substance. m is the mass of the substance. Q is the heat or energy of the substance. L f Latent Heat of F(change between solid and liquid. L v Latent Heat of Vaporization (change between liquid and gas) L s Latent Heat of Sublimation (change between solid and gas phases)

 Q is the symbol for heat. Heat is an exchange of energy.  In this chapter you were given several equations for heat (Q).  Remember that Q = Q and these equations can be set equal to one another in many cases.  Substance react differently to changes in temperature and experience different energy exchanges (heat) depending on their chemical composition.