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What occurs during a chemical reaction?
During a chemical reaction, substances react to produce new substances with different properties from the original substances.
The reaction that powers the space shuttle is a simple reaction. What are the reactants and products for this reaction?
The reactants are hydrogen and oxygen. The products are water and energy.
What are the reactants and products when you take an antacid for an upset stomach?
The reactants are magnesium hydroxide and hydrochloric acid (stomach acid). The products are magnesium chloride and water.
Note: Some antacids contain calcium hydroxide instead of magnesium hydroxide. The products would then be calcium chloride and water.
How do you know a chemical reaction occurs when a banana ripens?
You know that a chemical reaction has occurred when bananas ripen because the skin turns from green to yellow to brown.
Explain how bananas ripen.
Bananas release a ripening gas called ethylene, which triggers enzyme production. This, in turn, triggers colour change and softens the bananas.
Which substances are the active whitening ingredients in bleach?
Hydrogen peroxide or sodium hypochlorite are the active whitening ingredients in bleach.
Which common element is present in these whitening ingredients?
Oxygen is the common element present in these whitening ingredients.
Describe the reactions that cause bread dough to rise.
To make bread, flour is mixed with yeast and water. The enzymes in the yeast break down the starch in the flour into glucose. Other enzymes react with the glucose to produce ethanol (an alcohol) and carbon dioxide. The carbon dioxide bubbles through the dough mixture, causing the dough to rise. When the dough is placed in the oven, the heat helps the carbon dioxide bubbles expand and make the bread light and airy.
What gives freshly baked bread its delicious flavour? The alcohol released into the dough burns off, leaving a delicious flavour.
Read “Did You Know?” on page 25. Describe the process of digesting carbohydrates, fats, and proteins that involves enzymes.Digestion begins in the mouth, wher e an enzyme called amylase breaks down starches into simple sugars. In the stomach, an enzyme called protease speeds up the breakdown of proteins into amino acids. Next, partially digested food goes into the small intestine. Here an enzyme called lipase breaks down fats into glycerol and fatty acids.
If you’ve been to a swimming pool, particularly an indoor swimming pool, you probably noticed a distinct odour of chlorine in the air. To see how chlorine works to kill micro-organisms in a swimming pool, read “Swimming Pool Scent” on page 25 of the textbook. Which substance is produced when chlorine is added to water?
Hypochlorous acid is produced when chlorine is added to water.
What protection should people wear when working with chlorine?
People should wear rubber gloves and eye protection when using chlorine.
Many kitchen and bathroom cleaners contain chlorine. Obtain a number of cleaners that contain chlorine. List the warning symbols on these containers.
These containers usually contain the “corrosive contents” symbol.
Answers will vary. Your predictions for each part should be similar to the following:
Part 1: The limewater will turn milky if carbon dioxide is present.
Part 2: If hydrogen is present, there will be a “pop” or “squeal” when the burning splint is inserted into the test tube.
Part 3: If oxygen is present, the glowing splint will burst into flames when inserted into the test tube.
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Give three examples of combustion reactions that you encounter in a day.List as many of the reactants and products as you can.
Some combustion reactions are as follows:
natural gas burning in a furnace: The reactants are natural gas and oxygen. The products are carbon dioxide, water, and energy.
gasoline or diesel burning in an engine: The reactants are octane and oxygen. The products are carbon dioxide and water vapour.
a candle burning: The reactants are candle wax and oxygen. The products are carbon dioxide, water, and energy.
a lit lighter: The reactants are butane and oxygen. The products are carbon dioxide and water vapour.
Explain one neutralization reaction that occurs in the kitchen.
Answers will vary . One neutralization reaction that occurs in the kitchen is vinegar (or lemon juice) and baking soda. This reaction produces carbon dioxide gas, which makes cakes light and airy.
Fishy odours on your hands are caused by a base and can be eliminated with lemon juice. Is this an example of a combustion or a neutralization reaction? Why? What are the reactants?
This is an example of a neutralization r eaction because the reactants are an odour-causing substance of fish (an amine, which is a weak base) and an acid (lemon juice).
Describe a chemical change that occurs in nature. What is the evidence that a chemical change has occurred?
A chemical change that occurs in nature is the production of methane gas (marsh gas) in marshes or bogs. Bacteria produce the gas in these bogs when the oxygen level is low. The appearance of marsh gas over a bog is evidence of a chemical change.
Another chemical change that occurs in natur e is the decrease in production of chlorophyll in leaves of deciduous trees in the fall. The change of colour of these leaves is the evidence that chlorophyll is no longer produced and the chemical reaction to produce food is no longer occurring.
What evidence of a chemical change is shown in the pictures?
The appearance of the orange colour is the evidence of a chemical change.
After watching the segments on Investigating Chemical Reactions and after reading "Evidence of Chemical Change" on page 34, respond to the questions below.
List five pieces of evidence that show that a chemical change has occurred.
A different colour is produced.
An odour is detected.
Bubbles appear.
A solid (precipitate) forms.
Energy (such as light, heat, or sound) is given off.
Give an example where a colour change is the evidence of the reaction.
When bromothymol blue is added to hydrochloric acid, the colour of the solution turns yellow. Then when a Rolaids tablet is added to the solution, the colour changes to blue. This indicates that the solution has changed from acidic to basic.
Give an example where bubbles appear during the reaction.
When a small amount of hydrochloric acid is added to mossy zinc, bubbles appear on the surface of the zinc. Also, when manganese dioxide is added to hydrogen peroxide, bubbles appear.
What do you call the solid that forms as a result of combining two chemicals?
The solid is called precipitate.
Which chemical reaction has a nearly unnoticeable energy change?
Rusting has a nearly unnoticeable energy change.
Energy from burning gasoline in a car engine results mainly in which two types of energy?
Energy of motion (kinetic energy) and heat energy are the two types of energy that result from burning gasoline in a car engine.
Give two examples of an exothermic reaction and two examples of an endothermic reaction.
Examples of exothermic reactions are
burning gasoline in an engine
metabolism
rusting
Examples of endothermic reactions are
photosynthesis
ammonium nitrate dissolving in water (cold packs)
How do exothermic and endothermic reactions differ?
Exothermic and endothermic reactions differ in that energy is released in an exothermic reaction and absorbed in an endothermic reaction.
How are they similar?
Exothermic and endothermic reactions are similar in that both chemical reactions involve changes to the reactants to produce new products.
Some exothermic reactions can be quite dangerous. Give the reason behind the statement.
Exothermic reactions release energy. So if the amount of energy released is large and rapid, as in an explosion, the reaction can be quite dangerous.
Fossil fuel is combined with oxygen to produce carbon dioxide and water. We often thing of theses reactions as burning reactions. Are they exothermic or endothermic?
These reactions are exothermic because they release energy to provide motion or heat.
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