Introduction to Chemical Reactions
Theresa creates an experiment where she mixes two red-colored substances together in a container and observes the solution slowly changing from red to blue for the next eight minutes. The solution becomes completely blue after eight minutes. What does this represent about the type of change happening in the container?
A chemical change started immediately and finished at eight minutes.
Cherylanne mixes together Chemical A and Chemical B in a test tube, forming Chemical C. The mixture instantly turns cool to the touch. She then adds Chemical D, and the reaction becomes hot and explodes. What can be known about this situation?
Chemicals A and B form an endothermic reaction, and chemicals C and D form an exothermic reaction.
A Venn diagram is used to compare and contrast different topics. The items that are unique to each topic are represented in the separate sections of the circles, and the items that are common to both topics are represented in the center overlapping sections. Harlow creates this Venn diagram comparing and contrasting endothermic and exothermic processes. What can be added to the Examples section of each circle?
Endothermic: ice melting into water, and an instant ice pack turning cold
For a science project, Janet performs four experiments that are supposed to show a chemical reaction. She displays her results in a table. In the column titled "Chemical reaction?," which experiment's data should be changed to "No"?
Experiment 1
Chemical A and Chemical B react in an exothermic reaction. What can be known about what will happen when Chemical A and Chemical B are mixed together?
More energy will be released from the old substance than the new substance will need to form its chemical bonds.
Two chemicals react in an endothermic reaction. What can be known about this reaction?
The new substance will need more energy to form its chemical bonds than the old substance will release.
When vinegar and baking soda react, the mixture becomes cold to the touch and a gas and a new liquid substance are formed. Which best describes what is occurring in the reaction?
The reaction is chemical and endothermic.
Which actions are evidence that a chemical reaction has occurred? Check all that apply.
a change in color the formation of a precipitate a clear liquid becoming cloudy the formation of bubbles the formation of smoke
When baking soda and vinegar react, the surface bubbles. What does this most likely indicate?
a chemical change, because a gas is being formed
The Statue of Liberty is made out of copper and was once shiny and copper-colored. Over the years, the copper has gone through a process called oxidation, where it has changed into a new material. What has occurred?
a chemical reaction
Harvey mixes two liquids. Which observation of the new mixture most likely indicates a precipitate is forming?
a cloudy appearance
Which is an example of a chemical reaction?
paper burned and turned into smoke
A firework being ignited is an example of a(n) _
reaction.
When liquid silver nitrate and liquid sodium chloride are combined, solid silver chloride forms along with a new liquid, sodium nitrate. Which substance represents the precipitate?
silver chloride
Which best describes a chemical reaction?
the rearrangement of atoms by breaking and reforming chemical bonds
Reggie and Charlotte are baking oatmeal cookies. They dip the baked cookies in melted chocolate. The chocolate cools to form a hardened coating. Reggie argues the entire chocolate-covered cookie has undergone a chemical change. Charlotte disagrees, saying only the original oatmeal cookie has undergone a chemical change, not the chocolate coating. Who is correct?
Charlotte, because baking causes a chemical change, but melting objects is a non-chemical change.
Pedro wants to create a chemical reaction between oil and water. He adds oil to a beaker of water and notices that the liquids do not mix. He then shakes the beaker and the drops of oil become suspended through the water for a few moments before returning to their separate layers. Did Pedro succeed in creating a chemical change?
No, because no new substances were formed.
A(n) _ reaction is the rearrangement of atoms by breaking and reforming chemical bonds.
chemical
Which of these most likely represents a chemical change?
sugars digested by saliva
