Energy and Work
What is the difference between potential and kinetic energy?
Potential energy is stored energy, while kinetic energy is energy in motion.
Which has higher average kinetic energy: boiling water or ice?
Boiling water, because its molecules move faster.
Which type of reaction requires energy input to occur: photosynthesis or combustion
Photosynthesis (endothermic).
If 200 J of heat is added to a 50 g sample of water, and its temperature rises by 1°C, what is the specific heat capacity?
4 J/g·°C.
Which state of matter generally has the highest entropy: solid, liquid, or gas?
Gas
A book is sitting on a shelf. What type of energy does it have?
Potential energy
How does temperature differ from heat?
Temperature measures the average kinetic energy of particles, while heat is the total thermal energy transferred.
A chemical reaction releases light in addition to heat. Is this reaction exothermic or endothermic?
Exothermic
A reaction absorbs 75 kJ of energy. What sign does ΔH have?
Positive (endothermic reaction).
What happens to entropy when ice melts into liquid water?
Entropy Increases
According to the Law of Conservation of Energy, energy cannot be ______ or ______, only ______.
created, destroyed, transformed (or changed)
Why does a metal bench feel hotter than a wooden bench on a hot day, even though they are receiving the same amount of energy?
metal has a lower specific heat
What happens to the temperature of the surroundings during an exothermic reaction? Give an example.
The temperature increases. Possible example: Bonfires can be used to cook marshmallows!
Calculate the energy required to raise 100 g of iron from 20°C to 80°C. (c for iron = 0.45 J/g·°C)
2,700 J.
Does dissolving salt in water increase or decrease entropy? Why?
Increases entropy because ions disperse (separate and spread out) in solution.
A person pushes a box across the floor. What is the person doing?
Work!
Heat transfer occurs between two objects that have different temperatures until....
they are equal in temperature.
Give an example of an endothermic reaction used in everyday life.
Cooking an egg (absorbs heat).
(answers will vary)
A reaction releases 200 kJ of energy. If this energy is used to heat 5 kg of water, how much will the temperature increase? (c = 4.18 J/g·°C)
9.6°C
A reaction causes a solid to turn into a gas. Would you expect ΔS to be positive or negative? Why?
Positive, because gases have more disorder than solids.
A machine transfers 500 J of energy to lift a weight, but 50 J is lost due to friction. How much useful work was done?
450 J.
What is specific heat?
The amount of Energy (J) needed to raise 1g of an object by 1 degree C.
Explain the difference between system and surroundings, use an example in your explanation!
Answers will vary. System = the thing we are focused on in a given scenario; surroundings = everything else!
A chemical reaction heats 10g of water with 345 kJ of energy. What is the temperature change of the water? (c = 4.18 J/g·°C)
8.25°C
Is the entropy of the universe increasing or decreasing overall? Explain.
Entropy increases over time, as randomness/disorder are more common in nature. This is because there are more opportunities statistically for a group of molecules to be disordered than ordered/organized. Also, organizing molecules typically requires an input of work or energy.