Energy Assignment and Quiz
Chemical energy in burning wood is changed into thermal energy. The thermal energy is absorbed by water, which boils to produce steam. The thermal energy is changed into kinetic energy in the moving steam. The kinetic energy is used to turn a turbine, which converts the kinetic energy into electricity. Which sentence best describes this system?
It involves both energy transformation and energy transfer.
What happens to energy when Sally kicks a soccer ball?
Kinetic energy is transferred from the leg to the soccer ball.
Consider the following generic chemical equation: A + B → C + D Reactant A contains 85.1 J of chemical energy. Reactant B contains 87.9 J of chemical energy. Product C contains 38.7 J of chemical energy. If the reaction absorbs 104.3 J of chemical energy as it proceeds, how much chemical energy must product D contain? Explain your answer.
The law of conservation of energy states that energy is not created or destroyed during chemical reactions. The total amount of energy in the reactants, plus the energy absorbed during the reaction, must be equal to the total energy of the products. Product D contains (85.1 J + 87.9 J + 104.3 J) - 38.7 J = 238.6 J of chemical energy
Choose the best answer to each question. Which has the most kinetic energy? Which has the most thermal energy? Which has the least gravitational potential energy?
a bowling ball with a velocity of 1.5m/s a lake at 10°C a 10 kg barbell resting on the floor
Describe the energy transfers and transformations that occur when a person rides a bicycle. Make sure to identify each example as an energy transfer or an energy transformation.
chemical energy transformed to kinetic energy in muscles and/or body kinetic energy transferred from legs to pedals kinetic energy transferred from pedals to wheels kinetic energy transformed to thermal energy due to friction (wheels get warm) chemical energy transformed to thermal energy in muscles
Which energy change best relates to a boulder that is rolling down the side of a hill?
potential energy transforming into kinetic energy
A welding torch produces a flame by burning acetylene fuel in the presence of oxygen. The energy released from the acetylene fuel is then used to melt a metal. Which energy transformation happens during this process?
Chemical energy turns into thermal energy.
According to the law of conservation of energy, what will most likely happen in a closed system?
Energy will be exchanged, but matter will not be exchanged.
Old photographic flashbulbs burn magnesium metal in a reaction that causes a flash of brilliant white light. A photographer would need to take care not to suffer burned fingers when trying to replace the hot bulb. What best identifies the energy transformation that occurs in the flashbulb?
chemical energy to electromagnetic energy and thermal energy
Which is the best example of potential energy?
holding a basketball in the air
In a chemical reaction occurring in an open beaker, the reactants have a mass of 10.0 g and contain 1000 J of energy. The products in the beaker contain a mass of 5.0 g and 500 J of energy. Which best explains the difference in energy and mass as reactants are converted to products?
law of conservation
In a mechanical clock, the swinging of a pendulum causes the hands to move. The diagram shows the path of the pendulum as it swings. At which point in its swing does the pendulum have the least gravitational potential energy?
point C
What is the main form of energy represented by each of the following? A spring is compressed. Oxygen bonds with carbon. An electron generates an electric field. A soccer ball rolls along the grass.
potential energy chemical energy electromagnetic energy kinetic energy
Which statement describes thermal energy?
the energy that is associated with temperature
Which form of energy is directly related to the measure of the average kinetic energy of the particles in a substance?
thermal energy
