Energy and Phase Change Quiz

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Questions and Answers

What is the heat of fusion?

Energy required to convert a gas into a liquid

Energy required to convert a solid directly into a gas

Energy required to convert a solid at its melting point to a liquid (correct)

Energy required to convert a liquid into a solid

During a phase change, what happens to the temperature of the substance?

It decreases rapidly

It remains constant (correct)

It constantly rises

It fluctuates significantly

Which of the following is needed to calculate the heat during a phase?

Concentration of the substance

Pressure and volume of the substance

Phase identity of the substance

Specific heat, sample mass, and temperature change (correct)

What is the enthalpy change when converting 1.00 mol of ice at -25 °C to steam at 125 °C?

56.0 kJ Signup and view all the answers

Which statement is true about the heat of vaporization?

It's the energy required to turn a liquid at boiling point into a gas. Signup and view all the answers

What is the specific heat of liquid water?

4.18 J/g.K Signup and view all the answers

What is the formula to calculate the total heat during a phase change?

Mass x Specific Heat x Temperature Change Signup and view all the answers

What does the specific heat refer to?

The amount of heat required to raise the temperature of a substance per unit mass by 1 degree K Signup and view all the answers

What happens to the system's energy when a gas expands in a sealed vessel against atmospheric pressure?

The system loses energy as work is done. Signup and view all the answers

What sign indicates that energy is leaving the system as work?

Negative work indicates exit of energy. Signup and view all the answers

In the equation for work done by the system, which variable represents the change in volume?

ΔV Signup and view all the answers

If a system absorbs heat from the surroundings, what type of process is occurring?

Endothermic process Signup and view all the answers

How much work is done when the volume changes from 0.250 L to 0.980 L at a constant pressure of 1.35 atm?

29.83 J Signup and view all the answers

What is the defining feature of kinetic energy?

Energy that causes an object to move. Signup and view all the answers

What does the symbol ΔE represent in thermochemistry?

Change in internal energy. Signup and view all the answers

Which unit is used for measuring energy in the SI system?

Joule Signup and view all the answers

What does the term 'system' refer to in thermodynamics?

Molecules under study. Signup and view all the answers

How does heat transfer occur according to thermochemistry principles?

From warmer objects to cooler objects. Signup and view all the answers

Which of the following best describes potential energy?

Energy due to an object's position. Signup and view all the answers

What does thermochemistry specifically study?

Chemical reactions and their energy changes. Signup and view all the answers

What is the primary role of work in a chemical reaction?

To accompany heat changes. Signup and view all the answers

What is the calculated value of ΔH for the combustion of benzene (C6H6)?

-3267 kJ Signup and view all the answers

Which of the following enthalpy values corresponds to the combustion of propane (C3H8)?

-227.0 kJ/mol Signup and view all the answers

Using Hess's Law, what is the enthalpy of reaction for converting carbon to carbon monoxide (C to CO)?

-110.5 kJ Signup and view all the answers

What is the sign of the ΔH value for the combustion of carbon to CO2?

Negative Signup and view all the answers

What is the reaction equation for the combustion of carbon to yield CO2?

C(s) + O2(g) → CO2(g) Signup and view all the answers

How is the enthalpy for the combustion of CO adjusted using Hess's Law?

It is reversed and subtracted from that of C to CO2. Signup and view all the answers

What is the molar mass of benzene (C6H6)?

78.1 g/mol Signup and view all the answers

What value represents the enthalpy of formation (ΔHf) for carbon dioxide (CO2)?

-393.5 kJ/mol Signup and view all the answers

What is the relationship between enthalpy change and heat at constant pressure?

Enthalpy change is equivalent to the heat gained or lost. Signup and view all the answers

Which of the following definitions applies to specific heat capacity?

Energy required to raise 1 g of a substance by 1 K. Signup and view all the answers

How is the enthalpy of reaction, ΔH, calculated?

ΔH = Hproducts - Hreactants Signup and view all the answers

What instrument is used to measure heat flow in calorimetry?

Calorimeter Signup and view all the answers

In bomb calorimetry, what is primarily measured?

Internal energy, ΔE Signup and view all the answers

What does calorimetry allow us to measure directly?

The heat flow during a reaction Signup and view all the answers

What is the specific heat capacity value for water?

4.184 J/g∙K Signup and view all the answers

What signifies that a property is a state function?

It only depends on the current state, not the path. Signup and view all the answers

Study Notes

### Energy & Phase Change

Energy is either added or released during a phase change.
Phase changes include melting/freezing, vaporizing/condensing, and subliming/depositing.

Heat of Fusion, Vaporization, & Sublimation

Heat of fusion is the energy required to change a solid at its melting point to a liquid.
Heat of vaporization is the energy required to change a liquid at its boiling point to a gas.
Heat of sublimation is the energy required to change a solid directly to a gas.

Heating Curves

Temperature and heat added are plotted on a heating curve.
Within a phase, heat is the product of specific heat, sample mass, and temperature change.
During a phase change, the temperature of the substance does not rise.
For phase changes, heat is the product of mass and the heat of fusion or vaporization.

Calculating Enthalpy Change (ΔH)

Can be calculated for converting 1.00 mol of ice at -25 °C to steam at 125 °C under constant pressure of 1 atm.
Steps involved:
- Calculate enthalpy change for each individual phase
- Sum up the individual enthalpy changes to get the total enthalpy change (ΔHA→F)
Specific heats of ice, liquid water, and steam are 2.03, 4.18, and 1.84 J/g.K, respectively.
ΔHfus = 6.01 kJ/mol and ΔHvap = 40.67 kJ/mol for H2O.

Hess's Law

Definition: Enthalpy change for a reaction is independent of the pathway.
Can be used to calculate enthalpy of reaction for a reaction not directly measured if the enthalpy changes of other reactions are known.
Reactions can be reversed or multiplied to obtain the desired reaction.

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Description

Test your knowledge on the concepts of energy during phase changes, including heat of fusion, vaporization, and sublimation. This quiz will cover heating curves and the calculation of enthalpy changes, ensuring a comprehensive understanding of the subject.