Thermochemistry Quiz: Energy and Reactions

Which term describes a reaction that releases heat to its surroundings?

• Endothermic

• Exothermic

• Isothermal

• Adiabatic

Answer explanation

An exothermic reaction releases heat to its surroundings, making it feel warm. In contrast, endothermic reactions absorb heat, isothermal processes maintain constant temperature, and adiabatic processes involve no heat exchange.

Tags

NGSS.MS-PS1-4

Which of the following is always true for an endothermic reaction?

• The temperature of the surroundings increases.

• The system absorbs heat.

• The reaction releases light.

• The products have less energy than the reactants.

Answer explanation

In an endothermic reaction, the system absorbs heat from the surroundings, leading to a decrease in the temperature of the surroundings. Therefore, the correct statement is that the system absorbs heat.

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4

NGSS.MS-PS3-5

What is the SI unit for measuring heat?

• Joule

• Calorie

• Watt

• Kelvin

Answer explanation

The SI unit for measuring heat is the Joule. While calories are also used for heat measurement, Joules are the standard unit in the International System of Units (SI), making it the correct choice.

Which phase change requires energy to be absorbed from the surroundings?

• Freezing

• Condensation

• Melting

• Deposition

Answer explanation

Melting requires energy to be absorbed from the surroundings to break the bonds between solid particles, allowing them to transition into a liquid state. In contrast, freezing, condensation, and deposition release energy.

Tags

NGSS.MS-PS1-4

Which of the following best describes the temperature of a substance?

• The total energy of all particles

• The average kinetic energy of particles

• The amount of heat in a system

• The potential energy of particles

Answer explanation

Temperature is best described as the average kinetic energy of particles in a substance. It reflects how fast the particles are moving, which directly relates to the thermal state of the material.

Tags

NGSS.MS-PS3-4

Answer explanation

To calculate the heat absorbed by the water, use the equation q = m · c · ΔT, where m is mass, c is specific heat capacity, and ΔT is the change in temperature. This accounts for all necessary factors.

Tags

NGSS.MS-PS3-4

If 200 J of heat is added to a system and the temperature does not change, what is most likely happening?

• The system is undergoing a temperature increase.

• The system is undergoing a phase change.

• The system is losing energy.

• The system is exothermic.

Answer explanation

When 200 J of heat is added without a temperature change, the energy is used for a phase change (e.g., melting or boiling) rather than increasing temperature, making 'the system is undergoing a phase change' the correct choice.

Tags

NGSS.MS-PS1-4

Which statement best explains why the temperature remains constant during boiling?

• Heat is not being absorbed.

• Heat is used to break intermolecular forces.

• The system is losing energy.

• The pressure is decreasing.

Answer explanation

During boiling, heat energy is used to break intermolecular forces between molecules, allowing them to transition from liquid to gas. This energy input does not increase temperature, hence it remains constant.

Tags

NGSS.MS-PS1-4

A chemical reaction in a beaker causes the beaker to feel cold. What does this indicate about the reaction?

• It is exothermic.

• It is endothermic.

• It is at equilibrium.

• It is a combustion reaction.

Answer explanation

The beaker feeling cold indicates that the reaction absorbs heat from its surroundings, which characterizes an endothermic reaction. Therefore, the correct choice is that it is endothermic.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

Which of the following best distinguishes heat from temperature?

• Heat is a measure of energy transfer; temperature is a measure of average kinetic energy.

• Heat is measured in Kelvin; temperature is measured in Joules.

• Heat and temperature are the same.

• Heat is a measure of potential energy; temperature is a measure of total energy.

Answer explanation

The correct choice highlights that heat refers to energy transfer between systems, while temperature measures the average kinetic energy of particles in a substance, distinguishing the two concepts clearly.