FORMS OF ENERGY
Energy is the ability to do 2 things. What are they?
To do work or produce a change
What is the difference between energy transfer and energy transformation?
Transfer is energy moving from one object or place to another; transformation is energy changing from one form to another.
What type of reaction occurs when two or more simple substances combine to form a more complex substance?
A = B = AB
Synthesis reaction
State the law of conservation of energy.
Energy cannot be created or destroyed; it can only be transferred or transformed.
Water boils at 100°C under standard atmospheric pressure. Is boiling a physical or chemical change? Explain.
Physical change; the water remains H₂O.
A metal spoon becomes hot after sitting in a pot of hot soup. What form of energy has increased in the spoon?
Thermal energy
A hot mug of coffee cools down on a table. Explain how thermal energy is transferred.
Thermal energy transfers from the hotter coffee and mug to the cooler surroundings.
What type of reaction breaks a compound into simpler substances?
AB = A + B
Decomposition reaction
A student mixes two substances with a total mass of 75 g.
After the reaction, what should the total mass of the products be in a closed system?
75 g.
A student mixes vinegar and baking soda. The mixture bubbles and becomes cooler. Give two observations that suggest a chemical reaction occurred.
Gas production and a temperature change.
A flashlight uses batteries to produce light. What form of energy is stored in the batteries before the flashlight is turned on?
Chemical energy
A toaster converts electrical energy into what two forms of energy?
Thermal and radiant (electromagnetic) energy.
What type of chemical reaction involves oxygen?
Oxidation
A student mixes 20 g of substance A with 15 g of substance B in a sealed container. What is the total mass after the chemical reaction?
35 g.
A student claims that all energy transformations result in an increase in temperature. Explain why this is incorrect.
Energy can transform into other forms (as light, sound, or mechanical energy, etc) without necessarily increasing an object's temperature.
A sound wave travels through the air, and sunlight enters a room. What form of energy is associated with each?
Sounds energy --> radiant (electromagnetic)
When a metal spoon is placed in a pot of hot soup, thermal energy moves from the soup into the spoon. Is this an example of energy transfer or energy transformation? Explain.
Energy transfer ---> thermal energy moves from the hot soup to the cooler spoon.
Two clear solutions are mixed and a solid forms. What type of reaction has occurred?
Precipitation.
A student says that energy is destroyed when a battery runs out of power. Explain why this statement is incorrect.
The chemical energy stored in the battery is transformed into other forms of energy, such as electrical energy and thermal energy. Energy is not destroyed; it changes form.
A substance has a mass of 180 g and a volume of 60 mL. Calculate its density.
3 g/mL.
A moving car has mechanical energy, fuel contains chemical energy, and its engine becomes hot.
Identify the three forms of energy involved.
Mechanical, chemical, and thermal energy.
A battery-powered flashlight is switched on.
What FOUR energy transformations happen from the battery to the light produced.
Chemical energy transforms into electrical energy, which then transforms into electromagnetic energy and thermal energy.
What type of reaction is this?
2H2O --> 2H2 + O2
Decomposition
A student mixes vinegar and baking soda in an open container. The mass measured after the reaction is lower than before.
Explain why this does not necessarily violate the law of conservation of mass.
A gas is produced during the reaction and escapes into the air.
If all the products, including the gas, were contained and measured, the total mass would remain the same.
A solution contains 24 g of salt dissolved in 3 L of water. If 1 L of water is added, what is the new concentration of salt in g/L?
New volume = 3 + 1 = 4 L
Concentration = 24 g ÷ 4 L = 6 g/L