Chemistry 12 Unit 1

THERMOCHEMISTRY

Energy: the capacity to move matterUnits: Joule (J), calorie (cal)

Kinetic Energy  Potential Energy (KE)  (PE)The energy of motion  Energy that is stored

Thermal energy: due to kinetic energy (motion) of atoms/molecules

Temperature (t): measures average kinetic energy of particles on a relative scale.Units: Celsius (◦C), Kelvin (K)

(Absolute zero = 0K or -273 ◦C – no particle motion)

Heat: a transfer of kinetic energy from a higher temperature system to a lower temperature system

Thermochemistry is a study of the heat that is lost or gained during chemical reactions

Exothermic changes: heat is given off by the system

Endothermic changes: heat is taken in by the system

system

surroundings

System Effect on surroundings

Heat value of system

Endothermic Takes in heat Cools +

Exothermic Gives off heat Warms -

SPECIFIC HEAT CAPACITY (C)PREDICT/OBSERVE/EXPLAIN

Specific heat capacity is the amount of heat needed to raise the temperature of one gram of a substance one degree Celsius.

Basically, it is the ability of a substance to store heat energy. Different substances have different specific heat capacities. Water has a relatively high specific heat capacity, meaning that is takes a lot of heat to raise the temperature of water, while metals tend to have a low heat capacity.

In this experiment, the specific heat capacities of five different metals were compared. Equal weights of the metals were heated until all reached the same temperature. Each metal was then placed on a block of paraffin wax and allowed to cool. During cooling, heat energy is transferred from the metal to the block of wax, melting the wax and imbedding the metals into the block.

1. Which metal do you predict will melt the most wax and why?

2. Which metal do you predict will melt the least wax and why?

3. List the metals in order of depth in the wax.

(from most deep to least deep)

4. How does the specific heat capacity of a metal relate to the amount of wax it will melt while cooling?

5. Daryl and Cheri each designed a frying pan. They had to choose which metal to use. Daryl wanted his pan to reach a high temperature with the least amount of heat applied. Cheri wanted her pan to stay at a high temperature even when the heat was turned low. Which metal listed in the table would be best for Daryl, and which metal would be best for Cheri? Give reasons for your answers.

∆t = tfinal - tinitial

So, using this formula we can solve for any of the four variables. Rearrange the formula to solve for:

Mass (m)

Specific heat capacity (c)

Temperature change (∆t)

Example 1:

60.0 g of water at 26.5C is cooled to 9.70C. How much heat was lost by the water?

Example 2:

60.0 g of canola oil lost 4.0 x 103 J of energy, resulting in a temperature decrease from 35.0C to 5.2C. Calculate the specific heat capacity of the canola oil.

Homework:

1.Heat calculations worksheet2.Course expectations contract signed3.Lab Safety contract signed