Chemical Reactions Flashcards
Chemical reaction definition
A chemical reaction is a change that results in the formation of one or more new substance.
What are the two forms of equations in chemistry?
Give an example of these from the iron and sulfur reaction
Word equations and chemical equations.
Iron + sulfur —> iron sulfide
Fe + S —> FeS
What word do chemists use to describe an equation?
chemists use balance to describe an equation
definition of the law of conservation of mass.
Who discovered this law?
The law of conservation of mass states that when a chemical reaction occurs, the total mass of the reactants is always equal to the total mass of the products.
The French chemist Antoine Lavoisier discovered this.
How do we explain the law of conservation of mass? Give an example and the chemical formula
Lavoisier deduced that the mercury had reacted with the oxygen in the air to form mercuric oxide.
When Lavoisier opened the bell jar, he heard air ruching into the jar. He deduced that most of the oxygen had been used up, leaving a vacuum inside the jar.
When a metal such as mercury is heated in oxygen, there is an increase in mass. The extra mass comes from the oxygen gas that has combined with the metal.
Explain experiments if mass is unchanged when a physical or chemical change takes place
If a candle is lit and placed on a laboratory balance, we will notice that mass is not conserved, that is, the mass decreases as the candle is burned away.
the mass of the candle decreases as the wax burns and is converted into carbon dioxide and water vapour.
What rates do chemical reactions take place at?
Give an example of a fast and slow reaction.
Chemical reactions take place at different speeds.
Explosions are very fast reactions in which a large volume of gas is produced in a very short period of time.
The ripening of an apple or the rusting of iron are examples of very slow reactions.
What is the term ‘rate of reaction’ used to describe?
The term rate of reaction is used to describe how quickly chemical reactions occur.
Definition of the rate of reaction. the formula for the rate of reaction
the rate of reaction is defined as the change in concentration per unit time of any one reactant or product.
Change in concentration of anyone reactant or product
Rate of reaction = ——————————————————
Time taken
Catalyst definition
A catalyst is a substance that alters the rate of a chemical reaction but is not used up in the reaction.
Explain the experiment when hydrogen peroxide decomposers quickly to give off oxygen gas in the presence of magnesium dioxide.
the gas is collected in a graduated cylinder. This allows the volume of gas to be measured at regular times, for example, every half minute.
The manganese dioxide speeds up the rate at which the reaction occurs.
Manganese dioxide is an example of a catalyst.
Formula to find the average rate of reaction
Total volume of oxygen
Rate of reaction = ——————————————————
Total time for reaction to take place
What factors affect the rate of reaction? explain each.
Types of reactants:
Magnesium reacts quickly with hydrochloric acid while zinc reacts slowly with hydrochloric acid. The rate of reaction depends on the types of reactants together.
Particle size:
The reaction between marble chips and dilute hydrochloric acid. We will use small marble chips and large marble chips to compare the rates of reaction.
The rate of reaction depends on particle size. The smaller the particle size, the faster the rate.
Concentration:
Increasing the concentration of one or more reactants will often increase the rate of reaction. This occurs because a higher concentration of a reactant will lead to more collisions of that reactant in a specific time period.
Temperature:
An increase in temperature typically increases the rate of reaction. An increase in temperature will raise the average kinetic energy of the reactant molecules. Therefore, a greater proportion of molecules will have the minimum energy necessary for an effective collision. The higher the temp the faster the rate.
Catalysts:
A catalyst is a substance that increases the rate of a chemical reaction by lowering the activation energy without itself being consumed by the reaction. … A catalyst increases the reaction rate by providing an alternative pathway or mechanism for the reaction to follow.
The rate of reaction is altered by the presence of a catalyst.
Biochemical reaction definition. List some examples of biochemical reactions
A biochemical reaction is a chemical reaction that takes place in living cells, that is, a reaction in which new substances are formed.
What affects the rates of biochemical reactions?
The rates of biochemical reactions can be affected by:
Concentration:
of enzymes and of the substance on which the enzymes are acting. The general name given to the substance on which the enzyme acts is the substrate.
Temperature: many biochemical reactions only take place at specific temperatures.
pH:
Many enzymes only work within specific pH ranges. Outside these pH ranges, these enzymes become inactive
