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The Heat Equation
Julianna Hopkins 2005
The heat equation is used to determine the heat gained or lost during a reaction. deltaH=m*c*deltaT
deltaH- Change in energy
m- mass of system
deltaT- change in temperature (final - initial)
c- specific heat (found in book)
Procedures
Step 1: Identify your system and your surroundings. The system is what you are working with in the equation.
Step 2: Write equation and give values to the variables.
Step 3: Solve for x
Example 1
500 g of water is in a calorimeter. An endothermic reaction takes place. After the reaction, the temperature of the water in the calorimeter dropped from 34 degC to 24 degC. How much energy did the reaction take in?
Step 1:
Water=system
Reaction=surrounding
Step 2:
delta H = m*c*deltaT
deltaH: x (In this case deltaH will turn out to be negative, because our system is losing energy.)
m: 500g
deltaT: -10 degC (Final - Initail)
c: 4.2J/g*degC
Step 3:
deltaH = m*c*deltaT
x = (500g)(-10degC)(4.2J/g*degC)
x = -2.1*10^4J
Vocabulary to know:
endothermic- If a reaction is endothermic, it takes in energy to occur.
exothermic- If a reaction is exothermic it gives off energy while reacting.
Calorimeter- Inside a calorimeter, a reaction occurs inside a reaction chamber surrounded by a know mass of water. A calorimeter helps us to solve these problems more easily.
specific heat- The amount of energy needed to raise 1g of a subtance up 1 degC.
Example 2
A sample of 100g of water gained 5kj of energy after an exothermic reaction took place, how many degrees centigrate did it go up?
answer: 1.25 degC