Thermodynamics

The law of conservation of energy describes how the amount of total energy can change in a closed system. Which of these statements correctly describes this law?

• The amount of kinetic energy in a system is a constant value.

• Energy can be converted from one form into another, but it cannot be created or destroyed.

• An object can have potential energy or kinetic energy, but not both at the same time.

• The amount of energy created when an object moves is equal to the energy destroyed when it stops moving.

The graph below represents the relationship between the temperature of 2.0 kilograms of a pure substance and the heat energy added to the substance.

• AB, only

• BC, only

• BC and DE

• AB and CD

A substance of mass 2.0 kilograms is originally in the solid state. The graph below represents the temperature of the substance as heat is added to it. During which interval is the average kinetic energy of the molecules of the substance unchanged?

• BC

• CD

• AB

• AC

How is temperature related to heat?

• Temperature is a measure of the heat of an object.

• Heat causes a change in the temperature of an object.

• Raising the temperature causes the heat of an object to increase.

• Temperature and heat are two different ways to measure the same thing.

Zara is warming a pot of soup on the stove. How is the motion of the particles in the soup different after the temperature of the soup increases?

• They move faster on average.

• They have less average energy.

• They move less freely.

• They vibrate and are close together

Sonia notices that the temperature in the science lab is much colder than the temperature in her history classroom. Which of the following is true?

• The air molecules in the science lab are moving faster than those in the history classroom.

• The air molecules in the science lab are moving slower than those in the history classroom

• The air molecules in the science lab are moving at the same speed as those in the history classroom.

• The air molecules in the science lab are not moving while those in the history classroom are moving

In what type of reaction do the products of the reaction always possess more potential energy than the reactants?

• redox

• exothermic

• spontaneous

• endothermic

Assume that the potential energy of the products in a chemical reaction is 60 kilojoules. This reaction would be exothermic if the potential energy of the reactants were

• 20 kj

• 30 kj

• 50 kj

• 80 kj

Which phase change is exothermic?

• H 2O( l) → H 2O( s)

• H 2O( l) → H 2O( s)

• H 2O( l) → H 2O( g)

• H 2O( s) → H 2O( g)

How many joules of heat are required to raise the temperature of 20.0 grams of water from 30.0°C to 40.0°C?

• 42 kj

• 84 kj

• 420 kj

• 840kj