ENERGY AND CHEMICAL CHANGE

Chapter 15

ENERGY

ENERGY:

-the ability to do work or produce heat. 2 different forms: potential and kinetic

-Measured in Joules (J)

CHEMICAL POTENTIAL ENERGY:

-the energy stored in a substance because of its composition

HEAT:

-energy that is in the process of flowing from a warmer to a cooler object

-SI unit is Joules (J)

calorie (cal): the amount of energy required to raise the temperature of one gram of pure water by 1°C

*a nutritional Calorie is capitalized 1 nutritional Calorie = 1000 calories

1 nutritional Calorie = 1kilocalorie (kcal)

ex. 1tbsp. of butter contains 100 Calories. So if the butter is burned completely to produce carbon dioxide and water, it will produce 100000 calories of heat.

1 Joule = 0.2390 calories

1 calorie = 4.184 Joules

Q: A breakfast of cereal, oj, and milk might contain 230 nutritional Calories. Express this energy in joules.

9.6 x 10^5 joules

Specific Heat: amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

Specific heat of water is 4.184 J/(g ·°C) this means that 4.184 J of heat must be absorbed by every gram of water to raise the temperature 1°C

Each substance has its own specific heat (page 520)

Q: which has to absorb more heat to increase it’s temperature 1°C, water or concrete? So which gets hotter faster?

q = m x c x ∆T

q = heat absorbed or released. Measured in joules (J)

m = mass of the sample. Measured in grams (g)

c = specific heat. Measured in J/(g ·°C) (usually found on chart or given to you)

∆T = change in temperature. T(final) – T(initial) Measured in °C

Ex. If the temperature of 34.4g of ethanol increases from 35°C to 78.8°C. How much heat has been absorbed by the ethanol? Table 15.2 tells us that the specific heat of ethanol is 2.44 J/(g ·°C)

CALORIMETER

Insulated device that is used for measuring the amount of heat absorbed or released during a chemical or physical process.

-A known mass of water is placed in the insulated chamber to absorb the energy released from the reacting system or the provide the energy absorbed by the system. This data allows scientists to determine nutrional Calories in food.

http://bit.ly/ripNmk

THERMOCHEMISTRY: The study of heat changes that accompany chemical reactions and phase changes.

Ex. Burning of fuels always produces heat

Ex: Heat pack 4Fe + 3O2 → 2Fe2O3 + 1625KJ

System: specific part of universe that contains the reaction you wish to study.

Surroundings: everything in the universe other than the system.

Enthalpy: the heat content of a system at constant pressure

ENTROPY

-a measure of the number of ways that the energy of a system can be distributed. The disorder, randomness of particles that make up a system.

Which has more entropy a solid or a gas? Why?