Changes in Energy on a Molecular Level and Heat & Matter

Changes in Energy on a Molecular Level and Heat & Matter

Test Review

​But first, review!

​Atoms, Molecules and Compounds, and Extended Structures

Multiple Choice

Which of the following is true about how hydrogen and oxygen can combine to form molecules?

• When oxygen combines hydrogen, water molecules will ALWAYS be produced

• Molecules of hydrogen and oxygen must have at least 4 atoms

• Hydrogen and oxygen can combine in many ways to form different molecules

• 2 atoms of hydrogen are always required to bond with 2 atoms of oxygen

​Forming Molecules

​Oxygen (O) atoms can combine with hydrogen (H) atoms in many different ratios to form many different molecules!

• ​Water is 2 H atoms and 1 O atom (H₂O)

• ​Hydrogen peroxide is 2 H atoms and 2 O atoms (H₂O₂)

• ​The difference in ratios of H atoms to O atoms creates different molecules

Multiple Choice

Which of the following is an element?

Multiple Select

Which of the following is a molecule? (Can be more than one answer!)

Multiple Choice

Which of the following is a compound?

​Molecules are made up of 2 or more atoms

​Molecules can be made up of 2 or more of the same atom (example: O₂), or two or more different atoms.

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​Compounds can only be made up of two or more different atoms (2 different elements)

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All compounds are molecules, but not all molecules are compounds!

​(O₂ is a molecule but not a compound, CO₂ is a molecule that is also a compound)

Each state of matter (solid, liquid, gas) has a distinct set of characteristics and pattern of particle movement​

​Changes in Energy on a Molecular Level (States of Matter)

​Solid- Definite shape and volume; shape and volume is not affected by container it is in

​Liquid- Indefinite shape but definite volume; shape is determined by its container, but volume is not

Gas- Indefinite shape and volume. Shape and volume are determined by its container

Molecular Motion​

​Solid- Particles/molecules jiggle (vibrate) but do not move from place to place

Liquid- Particles/molecules vibrate and move freely past each other

Gas- Particles/molecules vibrate rapidly, move past each other at high speeds, and collide with each other and the walls of their container

Multiple Choice

As heat (thermal energy) is added to a substance, what happens to the particles of that substance?

• The particles slow down

• The particles speed up

• Adding heat does not affect the speed of the particles

Multiple Choice

Based on your answer for the previous question, what then happens to the kinetic energy of the particles?

• The kinetic energy decreases

• The kinetic energy increases

• The kinetic energy does not change

Multiple Choice

Based on your answer for the previous question, what then happens to the temperature of the substance?

• The temperature decreases

• The temperature increases

• The temperature stays the same

​Temperature and Kinetic Energy

​Kinetic energy is the energy of motion

• ​Each molecule of a substance has its own value for KE

• Temperature is a measurement of the average kinetic energy for each molecule in a sample of a substance

• ​As thermal energy is added, the molecules speed up

  • ​This increases the average kinetic energy, which we measure as an increase in temperature

• ​As thermal energy is removed, the molecules slow down

  • ​This decreases the average kinetic energy, which we measure as a decrease in temperature

Open Ended

Explain how we know that the molecules in a beaker of hot water are moving faster than those in a beaker of cold water using evidence from our food coloring in water demonstration. 

​Thermal Energy Transfer

​The transfer of thermal energy moves from one substance to another is dependent on the temperatures of the two substances

• ​Heat moves from areas of higher temperatures to areas of lower temperatures

• ​This continues until the temperatures of both areas are the same

Open Ended

Describe the movement of thermal energy between the beakers of hot water to the beakers of room temperature water from our demonstration on Tuesday, 9/28.

Multiple Choice

Thermal energy is removed from a sample of helium. All of the following changes will result from this EXCEPT–

• the molecules will become more packed.

• the temperature of the system will decrease.

• total energy in the system increases.

• the molecules of the system will lose kinetic energy.

Removing ​thermal energy from a substance will:

• Cause the molecules ​to become more closely packed together

• ​Cause the temperature to decrease

• ​Cause the molecules of the system to lose kinetic energy

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​It will NOT:

• ​Cause the total energy of the substance to increase

Poll

How prepared do you feel for your test next Monday?

• Not at all prepared

• Kinda prepared

• Mostly prepared

• Completely prepared and ready to go