chemical reactions Flashcards
When does a chemical reaction occur?
A chemical reaction occurs when the atoms of one or more substances are rearranged to produce one or more different substances
What is the result of a chemical reaction?
New substances with new properties will be formed
What is a reactant
A starting material for a chemical reaction
What is a product
A material produced from a chemical reaction
What is the general representation of a chemical reaction (hint: it’s simpler than you think)
reactants -> products
During chemical reactions, do reactions change directly into the products?
No, it takes time and energy for chemical bonds to be broken and made and the reactants are rearranged in multiple ways until they reach the final product.
What is a reaction pathway
The path that atoms and molecules have to follow for the reactants to turn into products. Reactants have to progress along the reaction pathway, changing energy as it goes, until it reaches the final product.
What changes as the reactants change and bonds are broken and remade?
The total energy of the reactants
What is a reaction coordinate diagram?
A diagram that plots the energy of the reaction versus how much time has progressed
When are atoms and molecules more stable?
When they have less energy
When are atoms and molecules less stable?
When they have more energy
What state (of energy) do chemical compounds try to move towards? Why?
A state of low energy, because it’s more stable
What is ΔE? (definition)
The overall change in energy from the beginning to the end of a reaction.
What is the formula for ΔE?
ΔE = (energy of products) - (energy of reactants)
What is Ea? (definition)
The activation energy of a reaction, or the smallest amount of energy necessary to start a chemical reaction.
Do all chemical reactions need Ea?
Yes. Activation energy is necessary to break the bonds of the reactants and form the bonds of the products. It is also necessary to start the reaction by overcoming the energy barrier.
What is the formula for Ea?
Ea = (energy of transition states) - (energy of products)
What is the transition state?
The state where the bonds of the reactants are breaking and the bonds of the products are forming. The highest in energy, used in order to get to the products.
What is an exothermic reaction?
A reaction that produces energy, often heat, light or sound
What is the formula of an exothermic reaction?
A+B=c+d+energy
What is an endothermic reaction?
A reaction that needs energy to happen, so they take energy from their surroundings
What is the formula of an endothermic reaction?
A+B+energy=C+d
Are the products of an exothermic reaction more or less stable than the reactants?
More stable
Are the products of an endothermic reaction more or less stable than the reactants?
Less stable
When is ΔE positive or negative?
ΔE = (energy of products) - (energy of reactants)
Positive in endothermic reaction
Negative in exothermic reaction
Is every reaction that requires some energy to start an endothermic reaction?
No. A reaction is exothermic if the amount of Ea is less than the amount of energy released, and a reaction is endothermic if the amount of energy released is less than the amount of Ea.
What kind of reaction does a less stable allotrope go through to become a more stable allotrope?
Exothermic, because it needs to release energy to become more stable.
What is a potential reason that a less stable allotrope might not react and become a more stable allotrope?
The reaction might have a high activation energy
Do reactions occur at different rates?
Yes. Different reactions occur at different rates, and the same reaction might occur at a different rate depending on the conditions.
What is chemical kinetics?
The field of science that studies the rates of chemical reactions. answers question “how fast will this occur?”
What 3 things must happen for a reaction to occur?
1) particle of reactants must collide w/ each other
2) particles must possess enough activation energy/must be going a certain speed
3) must have the right “orientation”
What is “collision theory”
Collision theory states that the frequency of particles colliding with each other successfully and reacting determines the reaction rate.
How can the rate of a chemical reaction be increased? (3 and give explanations)
Concentration: more particles in a smaller space = more likely to collide
Temperature: more speed/moving faster = more likely to collide
Catalyst: Decreases the amount of energy necessary for the reaction to happen, makes it easier
What is a catalyst?
- substance that changes the rate of a reaction
- same amount and identity post-reaction
- lowers the activation energy
- makes it so that it is more likely particles will have enough energy to react when they collide
For the average reaction occurring at room temp, the raising the temp by 10 degrees celsius ___ the reaction rate.
Doubles the reaction rate
