Chemistry Test #2 Third Quarter Grade 9 Flashcards
Percent Yield
The ratio of actual yield to theoretical yield, multiplied to 100%
Actual Yield/Theoretical Yield x 100
Reasons why we might not make as much product
Reactant might not all react (if reaction is slow/its a reversible reaction)
There may be some side reactions (reactants produce a different product then expected)
Lose some product during the process (Filtering: might not capture all of the liquid or solid)
Actual Yield
The amount we actually get.
Theoretical Yield
Yield we would expect to get based on our calculations.
0%
Don’t get any product
100%
All the product predicted
Collision Theory
A model to help us understand what is happening at the atomic level when reacting particles collide.
The three conditions for a reaction to occur
The reacting particles must collide with each other.
The colliding particles must have the correct orientation at the time.
The particles must have the minimum kinetic energy required to initiate a reaction.
Lower Concentration
Fewer particles to collide means less collisions.
Fewer successful collisions results in less product in same time.
Slower rate of reaction.
Higher Concentration
More particles to collide means more collisions.
Greater chance of successful collisions results in more product made in same time.
Faster rate of reaction.
Concentration…
affects the rate of reaction.
Exothermic Reaction
A chemical reaction during which heat is released into the surroundings (releasing heat out - warmer)
Making ice cubes - the water can be put in the freezer, where it releases its heat and forms into a solid.
Bringing candle - When the candle burns, it reacts with atmospheric oxygen and breaks hydrocarbon bonds. These changes release a good amount of energy, and therefore, it feels warm around the burning candle.
Activation Energy
the minimum amount of energy colliding particles need for a collision to be successful, and for a reaction to occur.
Endothermic Reaction
A chemical reaction during which heat is absorbed from the surroundings (absorbing heat - cooler)
Catalysts
A substance that increases the rate of a chemical reaction without itself understanding any permanent chemical change, by lowering the activation energy.
Enzymes
Are biological catalysts.
Enzymes speed up (catalyze) chemical reactions in cells.
They lower the threshold necessary to start the intended reaction. They do this by binding to another substance known as substrate.
Features of Activation Energy
Temperature dependent.
SI unit: kg/mol
Determined experimentally using the Arrhenius equation.
The minimum energy barrier reactant particles must overcome in order to react.
Rates of Reaction
Is a numerical description of the rate at which reactants are converted into products.
Reaction Rate = change in mass of reactant/product over time (s)
Reaction Rate Graphs
The progression of a reaction can be graphically represented, allowing you to make calculations of the initial rate of reaction.
Units
Gas: cm3s-1 (cubic centimeters (millimeters) per second)
Aqueous solutions: mol dm-3 s-1 (moles per cubic diameter (or liter) per second)
Two types of Rate of Reaction
How fast the reactants are being used.
How fast the products are being formed.
What influences the rate of reaction
Change in temperature (higher temperature for faster, lower temp for slower)
Presence or absence of catalysts (faster in the presence of, slower in the absence of)
Change in concentration of reactants (more reactants for faster reaction, less for slower)
Change in surface area (more SA means more reactants can interact)
