Chemistry - Chains, Energy and Resources - F322 - Energy (3) Flashcards
Define chemical energy.
Chemical energy is a special form of potential energy that lies within chemical bonds.
Define ethalpy, H.
Ethalpy, H, is the heat content that is stored in a chemical system.
Define exothermic.
Exothermic refers to a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (ΔH-ve)
Define endothermic.
Endothermic refers to a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken from the surroundings (ΔH+ve)
What is probably the most important exothermic reaction for life?
Respiration is probably the most important exothermic reaction for life.
What is probably the most important endothermic reaction for life?
Photosynthesis is probably the most important endothermic reaction for life.
Define the activation energy.
Activation energy is the minimum energy required to start a reaction by the breaking of bonds.
Once an exothermic reaction begins, what is regenerated making the reaction self-sustaining?
Once an exothermic reaction begins, the activation energy is regenerated and the reaction becomes self-sustaining.
What is the standard conditions of pressure?
Standard pressure is 100kPa (1 atmosphere)
What is the standard conditions of temperature?
Standard temperature is 25oC or 298K
What is the standard conditions of concentration?
Standard concentration is 1.0moldm-3 (for reactions with aqueous solutions).
What is the symbol for standard enthalpy change?
ΔHθ is the symbol for standard enthalpy change.
Define the standard state.
The standard state is the physical state of a substance under standard conditions of 100kPa and 298K
Define the standard enthalpy change of reaction, ΔHCθ
The standard enthalpy change of reaction, ΔHθC is the enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in standard states
Define the standard enthalpy change of combustion, ΔHθ
The standard enthalpy change of combustion, ΔHθ, is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states.
Define the enthalpy change of formation, ΔHfθ
The standard enthalpy change of formation, ΔHfθ, of a compound is the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.
What is the standard enthalpy change of formation of an element?
The standard enthalpy change of an element is defined as 0kJmol-1
What equations determines the heat exchange with the surroundings?
Q=mcΔT joules.
Where m is the mass of the surroundings
c is the specific heat capacity of the surroundings
ΔT is the temperature change of the surroundings
Define the specific heat capacity.
Specific heat capacity, c, is the energy required to raise the temperature of 1g of a substance by 1oC
Is the breaking of bonds endothermic or exothermic?
Breaking of bonds is endothermic, energy is required to break them.
Is the formation of bonds endothermic or exothermic?
The formation of new bonds is exothermic, energy is released.
In an exothermic reaction, are the bonds formed stronger or weaker than the ones broken?
In an exothermic reaction, the bonds that are formed are stronger than the bonds that are broken.
In an endothermic reaction, are the bonds formed stronger or weaker than the ones broken?
In an endothermic reaction the bonds that are formed are weaker than the bonds that are broken.
Why is it not always possible to measure the enthalpy change of reaction directly?
- a high activation energy
- slow reaction rate
- more than one reaction taking place
What does Hess’ Law state?
Hess’ law states that if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.
The rate of a chemical reaction can often be altered by…?
- temperature
- pressure, where the reactants are gases
- concentration
- surface area
- adding a catalyst
What does collision theory state?
Collision theory states that a chemical reaction will only take place when the reactants collide, the required activation energy is met and the molecules are in the correct orientation.
How does increasing the reactants affect the rate of reaction?
Increasing the concentration of reactants increases the rate of reaction
How does increasing the pressure affect the rate of reaction?
Increasing the pressure increases the rate of reaction because the same number of molecules occupies a smaller space, which leads to more collisions.
What is used as the catalyst in the Haber process?
Iron is used as the catalyst for the Haber process.
What is used as the catalyst in the contact process?
V2O5 is used as the catalyst in the contact process.
What is used as the catalyst in the hydrogenation of margarine?
Nickel is used as the catalyst in the hydrogenation of margarine.
How do catalytic converters improve air quality?
Catalytic converters improve air quality by reducing toxic emissions from vehicles and preventing photochemical smog.
Define heterogeneous catalysis.
Heterogeneous catalysis is catalysis of a reaction in which the catalyst has a different physical state from the reactants; frequently reactants are gases whilst catalysts are solids.
Define homogeneous catalysis.
Homogeneous catalysis is catalysis of a reaction in which the catalyst and reactants are in the same physical state, which is most frequently the aqueous or gaseous state.
What is biocatalysis?
Biocatalysis is catalysis where the catalyst is an enzyme.
How does the industrial use of enzymes have benefits?
- lower temperatures and pressures can be used than with inorganic catalysts
- enzymes often allow a reaction to take place that forms pure products
- conventional catalysts are often poisonous, enzymes are biodegradeable
In a Boltzmann distribution, what is the area under the graph equal to?
In a Boltzmann distribution, the area under the graph is equal to the total number of molecules in the sample
What happens to a Boltzmann distribution under increased temperature?
With increasing temperature, the distribution flattens and shifts to the right.
Define dynamic equilibrium.
Dynamic equilibrium is the equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction.
What does le Chatelier’s principle state?
le Chatelier’s principle states that when a system in dynamic equilibrium is subjected to a change, the position of the equilibrium will shift to minimise the change.
