8.5E Chemical Reactions (Post)

In which of the following examples has a chemical reaction occurred?

• After putting liquid batter into a hot pan, the batter solidifies and begins to turn brown.

• After turning on a blender filled with fruits, the fruit is chopped up and mixed together.

• After taking a tray filled with ice cubes out of the freezer, the cubes begin to melt.

• After adding a spoonful of sugar to a mug of hot coffee, the sugar dissolves completely.

When vinegar and baking soda are combined, bubbles begin to form. Bubbles are evidence of a chemical reaction because they -

• pop when they are touched.

• show that a gas is forming.

• form at a fast rate.

• are generally transparent.

In an experiment, two flasks of unknown, clear liquids are combined in a beaker and the following observations are obtained:

• Solution color remains clear;
• The amount of solution in the beaker increased;
• Solution temperature changed from 10C to 20C; and
• Some of the liquid remained in the flasks.

How many of the listed observations indicate a new substance was formed?

• 1

• 2

• 3

• 4

Which of the following examples shows that a chemical reaction has occurred?

• Teeth chop up an apple slice into smaller pieces.

• Sugar placed in sugar water sinks to the bottom.

• A glass jar shatters into many pieces when dropped.

• Bleach gets rid of a ketchup stain on a white shirt.

Examine the graph below. A crystalline substance is added to a beaker filled with water. The crystals dissolve, and a precipitate is formed. The bottom of the beaker is too hot to touch. The temperature is monitored and the temperature data is shown on the graph below. At which time did the temperature first reach 65C?

• 0

• 40

• 80

• 120

An experiment is performed in which a crystalline substance is added to a beaker filled with room temperature water. The following observations are made:

I. The crystals dissolve

II. A precipitate is formed.

III. The bottom of the beaker feels warm to the touch.

IV. Bubbles begin forming within the water.

All of the observations are evidence of a chemical change EXCEPT -

• observation I

• observation II

• observation III

• observation IV

Which of the following equations is correctly balanced?

• N₂ + 3H₂ -> 2NH₃

• H₂ + O₂ -> 2H₂O

• 2Ag₂O -> Ag₂ + O₂

• N₂ + H₂ -> NH₃

An unbalanced equation is shown here. Below it is a diagram with four locations in the unbalanced equation labeled. The equation could be balanced by adding a number two (2) in which location?

• A

• B

• C

• D

Which equation below is correctly balanced?

• C₁₁H₁₁O₁₁ + 12O₁₁ -> 12CO₁₂+ 11H₁₂O₁₂

• C₁₂H₁₂O₁₁ + 12O₂ -> 12CO₁₂+ 11H₁₂O₁₂

• C₁₂H₁₂O₁₁ + 12O₂ -> 12CO₁₂+ 11H₁₂O

• C₁₂H₂₂O₁₁ + 12O₂ -> 12CO₂ + 11H₂O

According to the law of conservation of mass –

• matter is always created in a chemical reaction.

• matter is always destroyed in a chemical reaction.

• matter is created and then destroyed in a chemical reaction.

• matter is not created or destroyed in a chemical reaction.