Chem- Unit 3 Test
Which statement about exothermic reactions is accurate?
As reactants form products, the potential energy decreases.
Heat that flows by conduction is the transfer of thermal energy between substances in contact. What must occur for this to happen?
One system must have higher kinetic energy than the other system.
The temperature of a gas is increased. Which statement best explains the effect that this has on the motion of gas particles?
The average kinetic energy increases, and the particles collide more frequently.
Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true?
The gas molecules in both containers have the same average kinetic energy.
Which is the best term to use when describing the energy of position?
potential
What advantage does a heterogeneous catalyst provide over a homogeneous catalyst in industrial processes?
A heterogeneous catalyst can be easily separated from reactants.
Which statement describes a catalyst?
Catalysts provide a lower energy pathway for the reaction.
Which statement best describes the use of a catalyst in a fuel cell?
It increases reaction rates.
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.
Which statement defines activation energy?
It is the difference between reactant energy and maximum energy.
What overall effect does adding a catalyst have on a chemical reaction?
It speeds up the reaction.
A book is falling from the top shelf of a bookcase. Which statement correctly describes the change in the energy of the book?
The potential energy decreases as kinetic energy increases.
Which statement best describes the use of catalytic converters in automobiles?
They oxidize hydrocarbons to form less toxic gases.
Digby wants to determine how many calories are in his bag of chips. Which calorimeter should he use?
bomb calorimeter
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 of energy
The heat capacity of a sample should be divided by which quantity to find the specific heat capacity?
mass in grams
What type of energy is the sum of an object's potential and kinetic energy?
mechanical energy
Which defines the average kinetic energy of a system's particles?
temperature
Which statement describes thermal energy?
the energy that is associated with temperature
How does the potential-energy diagram for a reaction indicate whether the reaction is endothermic or exothermic?
An endothermic reaction has reactants that are lower in energy than products because energy is absorbed to form the products.
An ice cube is dropped into a glass of milk at 20°C. Which statement explains the transfer of kinetic energy (KE)?
Because milk has higher KE than ice, KE is transferred from the milk to the molecules of ice.
Which statement describes the law of conservation of energy?
Energy cannot be created nor destroyed, but it changes from one form to another.
Reactant P contains 50 J of energy, and reactant Q contains 35.3 J of energy. The reactants combine to form product PQ, which contains 104 J of energy. What is the energy transformation?
Energy is absorbed because the product has more energy than the reactants have.
Which statement is correct about the law of conservation of energy?
Energy is transferred when atoms are rearranged.
Which of the following statements describes how enzymes differ from ordinary chemical catalysts?
Enzymes catalyze select chemical reactions.
Which reaction is an example of heterogeneous catalysis?
Ethene gas reacts with hydrogen gas by using a nickel catalyst.
The specific heat of water is 4.18 J/(g*°C) and that of wood is 1.97 J/(g*°C). Which statement is correct?
Given equal masses, water will heat up less than wood if the same heat is added.
Which statement best describes an effect of using a catalyst in an industrial process?
It lowers energy requirements.
Which statement describes how a basic coffee cup calorimeter works?
It uses the mass and specific heat of water along with a thermometer to measure the gain or loss of energy when a substance is added.
A generator contains a coil that spins to produce an electric current. How is energy transformed by using a generator?
Mechanical energy is transformed to electromagnetic energy.
A student touches a freshly baked cake that was taken out of the oven. Which best explains why the cake feels hot?
Molecules in the cake are moving faster than molecules in the skin.
Which statement best describes why specific heat capacity is often more useful than heat capacity for scientists when comparing two materials?
Specific heat capacity is an intensive property and does not depend on sample size.
A hot metal plate at 150°C has been placed in air at room temperature. Which event would most likely take place over the next few minutes?
The air molecules that are surrounding the metal will speed up, and the molecules in the metal will slow down.
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
In what type of reaction or process does heat flow into the system?
endothermic
When ammonium chloride is dissolved in water, the beaker gets cold. Which type of reaction does this describe?
endothermic
What would be the greatest difference in using an open ceramic coffee mug rather than an insulated mug with a lid as a calorimeter?
exchange of energy with the surroundings
Which is the best example of potential energy?
holding a basketball in the air
Which is the best term to use when describing the energy of motion?
kinetic
What is thermal energy?
the kinetic energy of particles in a system
Which event is endothermic?
the melting of ice
Which statement defines specific heat capacity for a given sample?
the quantity of heat that is required to raise 1 g of the sample by 1°C (Kelvin) at a constant pressure
Which statement describes mechanical energy?
the sum of the kinetic energy and the potential energy of an object
