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What is Heat?
What is Heat?
Heat can be thought of as the amount of thermal energy entering or leaving a system from its surroundings. What's a system? Well, a system is anything that we are currently interested in. The surroundings are everything else.
For example, I could define a "system" as an ice cube and the "surroundings" will be my finger. Heat always flows from high to low. Therefore, heat is being transfered from my finger (the surroundings) to the ice cube (the system).
We define the heat entering the system from the surroundings as an endothermic change. (endothermic = enter)
The reverse would be heat exiting the system and going into the surroundings. We call this an exothermic change. (exothermic = exit)
what is Heat specifically?
what is Heat specifically?
Not everything transfers heat at the same speed. Some things like styrofoam transfers heat very slowly. Somethings, like many metals, transfer heat very fast. This is refered to as the substances specific heat capacity.
Heat equation
Heat equation
The amount of heat required to change the temperature of a substance is relative to the mass of the substance and the desired temperature change.
It can be given as this equation:
Q = mCpΔT
Q = heat
m = mass
Cp = specific heat of the substance
ΔT = change in temperature (final temp minus initial temp)
Phase changes
Phase changes
When you heat something up it generally changes the temperature. However, there are instances where this isn't the case.
When a substance goes through a change in state of matter (i.e. it freezes, melts, boils, or condenses) the heat does not change the temperature. Instead the energy goes into either breaking or making bonds between molecules.
The energy required for these phase changes is called the latent heat. It is proportional to the mass of the substance.
The rate of the latent heat is also different depending on whether it's melting/freezing or vaporizing/condensing. The heat of fusion or vaporization is given by the equation below:
Qfus = mΔHfus
Qvap = mΔHvap
m = mass
ΔHvap = heat of vaporization
ΔHfus = heat of fusion
ΔHvap water = 2260 J/g
ΔHfus water = 334 J/g
Practice
Practice
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