Thermochemistry Introduction Worksheet
Name: _______
KEY________
1. What is the difference between energy, heat, and temperature?
ENERGY – THE POTENTIAL OR CAPACITY TO MOVE MATTER (ABILITY TO DO WORK)
HEAT – THE TOTAL ENERGY OF ALL THE MOLECULAR MOTION INSIDE OF AN OBJECT
TEMPERATURE – MEASUREMENT OF THE HEAT OR THERMAL ENERGY AN OBJECT HAS
2. What is the primary difference between an endothermic process and an exothermic process?
ENDOTHERMIC – ENERGY GOES INTO THE SYSTEM
EXOTHERMIC – ENERGY GOES OUT OF THE SYSTEM
3. Write down the definition of these words as they relate to Thermochemistry.
- Energy
The ability (or capacity) of a system to do work
or supply (or produce) heat
- Work
The transfer of energy from one mechanical
system to another. (A force acting over a distance)
- Heat
Energy that transfers from one object to another
because of a temperature difference between them
- Temperature
Temperature indicates the direction in which energy
flows (as heat) when two objects are in thermal contact
- System
The part of the universe we wish to focus our
attention on
- Surroundings
The rest of the universe that is not the system
- Endothermic
Chemical reaction that is accompanied by the
absorption of heat into the system
- Exothermic
Chemical reaction that is accompanied by the
release of heat from the system
4. Name the following phase changes and identify each of them as either as endothermic or an exothermic.
Phase Change
Liquid Solid
Name
FREEZING
Endo- or ExoEXOTHERMIC
Gas  Solid
DEPOSITION
EXOTHERMIC
Gas Liquid
CONDENSATION
EXOTHERMIC
Solid Gas
SUBLIMATION
ENDOTHERMIC
Solid Liquid
MELTING
ENDOTHERMIC
Liquid Gas
VAPORIZATION
ENDOTHERMIC
5. Why does moisture condense on the outside of a glass of cold water?
When water vapor in the air comes into contact with something cool, such as the outside of a cold glass of
water, its molecules slow down and get closer together. When that happens, the energy from the warmer air
transfers into the cold glass causing the water vapor in the air to condense into liquid drops on your glass!
6. Distinguish between kinetic and potential energy in the following examples:
-
A jack-in-the-box - POTENTIAL ENERGY
-
An avalanche of snow – KINETIC ENERGY
-
Books on a library shelf - POTENTIAL ENERGY
-
A mountain stream - KINETIC ENERGY
-
A stock-car race - KINETIC ENERGY
-
A ham sandwich - POTENTIAL ENERGY
7. Describe the transfer of energy between the skin and the surroundings as a person perspires and the sweat
evaporates.
You sweat when your body gets hot to maintain stable internal conditions. The sweat (system) rests on your skin
(surroundings). Your body has heated up and is warmer than the liquid sweat that now rests on it. The warm
skin transfers its thermal energy INTO the sweat in an endothermic reaction causing the sweat to evaporate.
8. State what is wrong with the following statements.
-
If an exothermic reaction takes place in water, heat is absorbed from the water and the temperature of the
water increases.
IN AN EXOTHERMIC REACTION, HEAT WILL BE RELEASED INTO THE SYSTEM. THIS IS WHAT WILL CAUSE THE
INCREASE IN THE TEMPERATURE OF THE WATER. (WATER IS ABSORBED DURING AN ENDOTHERMIC REACTION)
-
Combustion reactions are usually endothermic.
COMBUSTION REACTIONS OCCUR WHEN THINGS BURN. BURNING RELEASES HEAT INTO THE SURROUNDING
AREA WHICH WOULD BE AN EXOTHERMIC REACTION.
9. Draw a glass of water with an ice cube floating at the top of the water. Label the system and its surroundings (is
the entire glass of water with the ice cube the system, or just the ice cube?). Describe what’s happening to the
energy in the water and the ice cube. Draw an arrow in the direction of the transfer of heat between the system
and its surroundings. Is this an endothermic or exothermic process?
THE WATER HAS MORE HEAT THAN THE ICE.
THIS CAUSES THE HEAT TO BE ABSORBED INTO THE ICE.
THE ICE WILL MELT AS IT ABSORBS MORE AND MORE HEAT.
THE WATER WILL COOL AS HEAT GOES INTO THE ICE.
THIS IS AN ENDOTHERMIC REACTION FOR THE ICE SYSTEM.