Chemical Reactions
The principle of conservation of mass is true
for reactions in both open and closed systems.
CaCO3 represents a chemical
formula.
A reaction in which one element replaces another in a compound or in which two elements in different compounds trade places is called a(n) ___________________ reaction.
replacement
A precipitate is a(n) ___________________ that forms from solution during a chemical reaction.
solid
In chemical reactions, what does the principle of conservation of mass mean?
Matter is not created or destroyed.
Explain which bonds are broken and which bonds are formed during the reaction of magnesium and oxygen to form magnesium oxygen. Identify which substances are compounds and which are elements. 2 Mg + O2----> 2MgO
The bonds between oxygen atoms in O2 are broken. Bonds form between magnesium and oxygen in MgO. Mg and O2 are elements, MgO is a compound.
What is the purpose of the burning splint in the reaction?
The burning splint provides activation energy needed to start the reaction between oxygen and hydrogen.
Which is the correct chemical equation for the following statement? Sodium reacts with oxygen in a 2 to 1 ratio for produce sodium oxide.
4 Na + O2 ----> 2 Na2O
When the candle was lit, a pool of liquid wax formed in the area around the wick, and then spilled over the side and solidified. Does this observation refer to a physical change or a chemical change? Explain.
A physical change. The substance was still wax, but it changed to a liquid and back to a solid.
Describe the difference between a synthesis reaction and a decomposition reaction.
A synthesis reaction produces a more complex substance from simpler substances. A decomposition reaction produces simple substances from a more complex substance. These two reactions are opposite processes.
Explain each of the following in terms of factors that affect the rate of a chemical reaction. (Extra Credit) A) Chemical reactions in living thingd would not be possible without the enzymes found in cells. B) Wood burns at a steady rate, but sawdust may explodr if a spark ignites it. (Sawdust is tiny particles of wood made from sawing wood.)
A) Enzymes are catalysts. They speed up chemical reactions by lowering the activation energy of reactions needed for life. Enzymes allow reactions that are neccessary for life to occur at body temperature. B) Sawdust has a greater surface area than wood. Increased surface area of a reactant will increase the rate of a chemical reaction. In this case, more of the reactant (sawdust) will come in contact with oxygen, so a spark is enough to start an explosion.
For each situation described below, tell whether the reaction is endothermic or exothermic. Explain your reasoning in terms of the energy of the reactants and products. A) A log burns in a fireplace, giving off gases and leaving behind ash. B) When vinegar and baking soda are mixed, new substances form and the solution becomes cooler.
A) The reaction is exothermic because heat and light are giving off. The energy of the products is less than the energy. B) The reaction is endothermic. Energy is absorbed by the reaction. The energy of the products is greater than the reactants.
If the products formed from the burning candle are mostly carbon (C), carbon dioxide (CO2), and water (H2O), what elements were in the reactants? How do you know?
Carbon, hydrogen, and oxygen. No matter is created or destroyed in a chemical reaction. If its in the products it must have been in the reactants.
Is the reaction that occurs in the diagram endothermic or exothermic? Explain.
Exothermic - heat and light are released as the candle burns.
Physical changes occur when existing bonds break and new bonds form.
False, chemical
The rate of a chemical reaction is independent of temperature.
False, dependent on
The amount of matter in a chemical reaction changes.
False, remains the same
Which of the following is an example of how to supply activation energy to begin a reaction?
Heat the reaction flask on a hot plate.
What type of chemical reaction represented in the diagram? Explain.
Synthesis, two elements, hydrogen and oxygen combine to form a compound, H2O.
Relate the writing and balancing of a chemical equation to the principle of conservation of mass.
The principle of conservation of mass states that matter cannot be created or destroy during a chemical reaction. Therefore, the number and kind of atoms going into a chemical reaction must exactly equal the number and kind of atoms coming out of the reaction. Balanced chemical equations must show that all the elements present in the reactants are present in equal amounts in the products.
A chemical reaction may be detected by observing changes in the properties of matter.
True
Synthesis is the process of making a more complex from simpler substances.
True
The ___________________ is the minimum amount of energy that must be added to start a chemical reaction.
activation energy
The ___________________ is the amount of one material present in a given volume of another material.
concentration
A bottle of hydrogen peroxide that eventually turns into a bottle of water and oxygen gas is an example of a
decomposition reaction.
Chemicals that act as biological catalysts by speeding up reactions in living things are called
enzymes.
A material used to decrease the rate of a chemical reaction is a(n)
inhibitor.
In a chemical equation, the substances written on the right side of the arrow are called ___________________.
products
The only sure evidence for a chemical reaction is
the production of one or more new substances.
Chemistry is
the study of matter and how matter changes.
