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Particle Models of Chemical Change 4 questions

Particle Models of Chemical Change

New Regents original practice • Name: ____________________ Date: __________ Show your work for written answers.

In a particle drawing, joined circles represent atoms bonded in one molecule. An atom’s label stays the same during an ordinary chemical reaction.

Question 1

A drawing shows three separate O₂ molecules. How many O atoms are shown?

  1. 2
  2. 3
  3. 5
  4. 6

Question 2

Explain the difference between 2H₂ and H₄ when reading a particle model.

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Question 3

What must be conserved in a closed chemical-reaction drawing?

  1. The number of molecules of every substance
  2. The number of atoms of each element
  3. The number of single bonds
  4. The distance between every pair of atoms

Question 4

A before panel shows two O atoms and an after panel shows three. Explain why they cannot both show all particles in the same closed reaction.

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Before and After a Model Reaction 4 questions

Before and After a Model Reaction

Use the information below to answer the questions.

The diagram represents a closed model reaction of hydrogen and oxygen. Connected atoms belong to the same molecule. Read each panel as a count of particles.

Before shows two H–H molecules and two O–O molecules. After shows two H–O–H molecules and one O–O molecule.
Particle counts before and after the model reaction.
Open full-size figure

Question 5

How many H₂O molecules form in the after panel?

  1. 1
  2. 2
  3. 3
  4. 4

Question 6

Count the H and O atoms in the before panel and in the after panel. Show whether the counts agree.

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Question 7

Which molecule remains unchanged in the after panel?

  1. H₂
  2. O₂
  3. H₂O
  4. All reactant molecules are used.

Question 8

Write a balanced equation for the molecules that react and the molecules they form. Use the diagram to explain how you treated the leftover O₂.

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