Ch. 2 Matter and EnergySection 1 Energy

Energy is a broad concept with many different definitions.

Energy is the capacity to so some kind of work; Moving an object Forming a new compound Generating light

Energy is always involved when there is a change in matter

Energy and Change

Both physical and chemical changes require energy

Sometimes energy must be supplied for a change to occur

Ex. Melting ice to water to boiling water to evaporation

Sometimes energy is released

Ex. Vapor turns into a liquid which then turns into a solid

Ex. The explosion that occurs when hydrogen and oxygen react gives off energy

Change in Matter involves a change in Energy

Endothermic – absorption of energy (heat) from the environment Ex. Melting of ice Formation of ice crystals when barium hydroxide and

ammonium nitrate react Exothermic – energy (heat) is released to the

environment Law of conservation of energy – during any

change the total quantity of energy remains constant; energy is never created nor destroyed

Endothermic and Exothermic Processes

There is a constant back and forth transfer of energy from a system (those materials being studied) to surroundings (outside of the system)

Exothermic – transfer from system to surroundings (release of energy)

Endothermic – transfer from surroundings to system (absorption of energy)

Total amount of energy between the systems and surroundings remains constant.

Energy is often transferred

Energy can exist and transfer between many different forms: Chemical, mechanical, light, heat, electrical,

sound

Ex. Light sticks – chemicals inside the stick react to release energy in the form of light which is transferred to its surroundings that we can see.

Energy is its forms

Heat is the energy transferred between objects of different temperatures Energy always moves from a warmer object to

a cooler object. Ex. Ice melts in water …water releases heat to

the ice causing it to warm

Heat

Energy was released as heat during an enormous explosion in Texas in April 1947 on a cargo ship (Grandcamp) that was carrying huge amounts of fertilizer

The fertilizer had stored chemical energy which was released via an exothermic chemical reaction in the form of heat and kinetic energy (energy of motion) which resulted in destruction or damage to all of the buildings in the city

Energy released as Heat

When you bake a cake you use either baking soda or baking powder which contain the chemical, sodium bicarbonate, that absorbs the heat of the oven in an endothermic reaction.

The sodium bicarbonate breaks down via a chemical reaction into sodium carbonate, water vapor and carbon dioxide gas…the CO2 causes the cake to rise.

Energy absorbed as Heat

Heat is energy is transferred from one object to another

This transfer of heat can be measured by calculating changes in temperature

Temperature- how hot or cold something is; the measurement of the average kinetic energy of the random motion of the particles of a substance

Heat vs. Temperature

Fahrenheit (not used in chemistry or physics)

Celsius – zero point is the freezing temperature of water

Kelvin – SI unit whereby the zero point is absolute zero; minimum average kinetic energy of all moving particles.

Temperature Scales

As ice melts into water in a sealed container the temperature remains at 0°C even though heat is being transferred during the melting process.

Once all the ice has melted, then the temperature will begin to rise.

Temperature does not increase as water goes through its phase changes.

Heat transfer may not affect temperature

Specific heat – the relationship between the energy transferred as heat to a substance and the substance’s temperature change

The specific heat of a substance is the quantity of energy as heat that must be transferred to raise a temperature of 1 g of a substance 1 K. (J/g ·K)

Metals have a low specific heat – get hot easily Water has high specific heat- takes a lot of

energy to raise the temperature

Transfer of Heat Affects Substances Differently