HEAT

TEMPERATURE AND HEAT Temperature Heat Measure of the average kinetic energy of the particles in a substance Heat The transfer of energy from one substance to another due to temperature differences Always from high E to low E

THE NATURE OF ENERGY Energy The ability to do work or produce heat 2 types: potential and kinetic

Potential Energy Potential energy - is the energy stored in a body or in a system

Kinetic Energy Kinetic energy - energy which it possesses due to its motion Depends on the mass of the object and its velocity

More Kinetic energy

More about Energy Law of Conservation of Energy Energy can be converted from one form to another but cannot be created or destroyed

So lets talk about heat…

We can measure heat… q = m x ∆T x c q = heat m = mass ∆T = change in temperature Tfinal – Tinitial c = specific heat capacity (specific heat) The quantity of heat required to raise temperature of an object 1oC

Using the formula We need 3 out of the 4 so we can solve for the 4th q = m x ∆T x c If have q, m, and c – what solving for? If have m, c, and ∆T – what solving for?

Value of “q” What is “q” – HEAT q can be positive or negative If q is positive – energy is added The reaction is endothermic If q is negative – energy is removed/leaving The reaction is exothermic

You said what?? Exothermic process: a change (ie. a chemical reaction) that releases heat. Ie: Burning fossil fuels Think “exit” Endothermic process: a change (ie. a chemical reaction) that absorbs heat. Photosynthesis is an endothermic reaction (requires energy input from sun) Think “into”

Sample Problem PCl3 is a compound used to manufacture pesticides. A reaction requires that 96.7 g of PCl3 be raised from 31.7 oC to 69.2 oC. How much energy will this require given that the specific heat of PCl3 is 0.874 J/g oC? A quantity of water is heated from 25.0 oC to 36.4 oC by absorbing 325 J of heat energy. What is the mass of the water? The specific heat of water is 4.184 J/g oC.

Heat Transfer

Heat Transfer Heat will transfer from one object to something else This is a transfer of energy from a place of high E to a place of low E The transfer of E will change the temperatures

Heat Transfer in Water… But what about temperature? Exothermic reaction: heat given off -temperature of water will increase -temperature of object will decrease UNTIL temperature of water and object are equal!! Therefore Tfinal for water and object are the same reaction

(con.) Endothermic reaction: heat taken in -temperature of water will decrease -temperature of object will increase UNTIL temperature of water and object are equal!! Therefore Tfinal for water and object are the same reaction

Therefore… - q lost = q gained We can say that: q lost = q gained But wait… one is going to be negative Therefore we must: - q lost = q gained

But what does q equal? -(m x ∆T x c) = m x ∆T x c - q lost = q gained q = m x ∆T x c Therefore we can say that: - q lost = q gained -(m x ∆T x c) = m x ∆T x c

Enthalpy of Fusion

Enthalpy of fusion: Hfus The energy needed to melt a solid into a liquid As energy is added to a solid at its melting point, all the energy is used to increase the kinetic energy of the molecules during the phase change. Because of this, the temperature of the melting system remains constant until all of the solid has become liquid. If energy is still being added to the system, the temperature will begin to climb when all of the solid becomes liquid.

Another way to look at it… When a solid melts, its particles are freed to move with respect to one another.

Formula (solid  liquid) Formula: q = m Hfus q = heat gained (+) or lost (-) m = mass DHfus = heat of fusion Formula for Heat Transfer with Enthalpy of Fusion m  Hfus = m  Tc

Enthalpy of Solution

Enthalpy of Solution The energy change when one mole of a substance dissolves in water. Formula: q = m  Hsol q = heat gained (+) or lost (-) m = mass  Hsol = heat of solution Formula for Heat Transfer with Enthalpy of Solution m  Hsol = m  Tc