L1 - Chemical Reactivity Flashcards
Define ‘energy’.
The ability to do work.
Define ‘work’.
The distance moved against an opposing force.
What is the equation for work?
Work = Force x Distance
What units is energy measured in?
Joules (J)
Define ‘1 Joule’.
The amount of energy required to raise a 1kg substance 10cm against the force of gravity.
Define ‘1 Calorie’.
The amount of heat necessary to raise the temperature of exactly one gram of water by one degree Celsius.
What are the conversions into kcal and cal for 1 calorie.
1 calorie = 1 kcal = 1000 cal
Describe potential energy.
- Stored energy
- Energy due to position
What is the equation for potential energy?
PE = mgh
Describe kinetic energy.
- Energy of motion
- Depends on mass and velocity
What is the equation for kinetic energy?
KE = 1/2mv^2
Describe chemical energy.
- Energy stored in bonds
State the 5 different types of energy.
- Potential energy
- Kinetic energy
- Electromagnetic energy
- Nuclear energy
- Chemical energy
State the ‘First Law of Thermodynamics’ / Law of Conservation of Energy.
“Energy cannot be created or destroyed by any physical and chemical changes - it can only be converted from one form to another.”
What are the conditions for chemical reactions to occur?
- Reactants energetic
- Reactants oriented correctly
Energy is either ________ or ________.
Energy is either released or absorbed.
What is the change in energy?
The difference between bond energies of reactants and products.
Enthalpy change of reaction (ΔH)
Define ‘enthalpy’.
A measure of the heat content of a substance at constant pressure.
What does ΔH° mean?
Heat released / absorbed during a chemical reaction at standard conditions
What is the equation for ΔH°?
ΔH° = H.products - H.reactants
What can you not measure?
Cannot measure the actual enthalpy of a substance (but can measure enthalpy change)
What is the standard state of an element?
- 1 atmosphere
- 25°C
What is the standard state of a compound?
- Gaseous substance = 1 atmosphere
- Pure substance in a condensed state (liquid / solid) = state it would have at 1 atmosphere
- Substance in solution = concentration of 1M
What is used to indicate physical state?
Subscripts:
- (g)
- (l)
- (s)
Describe the 3 characteristics of exothermic reactions.
- Negative ΔH
- Heat given out
- Enthalpy of reactants > products
Describe the 3 characteristics of endothermic reactions.
- Positive ΔH
- Heat absorbed
- Enthalpy of products > reactants
What will happen to the temperature of an exothermic reaction?
Temperature of the system will be observed to rise.
What will happen to the temperature of an endothermic reaction?
Temperature of the system will fall (in practice, reactants will be heated to speed up the reaction and provide the absorbed heat).
What happens during bond breaking?
Energy is added
What happens during bond making?
Energy is released
Define ‘entropy’.
Measures the amount of energetic disorder in a system.
When is entropy higher?
When the disorder / randomness of particles in a substance / mixture are greater.
What is the symbol of entropy?
S
What units is entropy measured in?
J mol^-1 K^-1
What is the equation for ΔS?
ΔS = S.final - S.initial
What is the equation for ΔS.total?
ΔS.total = ΔS.system + ΔS.surroundings
State the ‘Second Law of Thermodynamics’.
“Entropy tends to a maximum.”
What do all spontaneously occurring chemical and physical changes involve?
An overall increase in entropy.
Describe scenarios in which entropy is increased.
- Solids melting
- Liquids boiling
- Number of molecules increasing
- Ionic solids dissolving
- Temperature increasing
Define ‘Gibbs Free Energy’.
Energy from a reaction free to do work.
What is the equation for ΔG?
ΔG = ΔH - TΔS
What happens if ΔG < 0?
Reaction will be spontaneous
What happens if ΔG > 0?
Reaction needs energy input to occur
What happens if ΔG = 0?
System is in equilibrium
What is the quantity of ΔG if the reaction is spontaneous?
ΔG < 0
What is the quantity of ΔG if the reaction needs energy input to occur?
ΔG > 0
What is the quantity of ΔG if the system is in equilibrium?
ΔG = 0
What happens during catabolic reactions?
High energy compounds → Simple molecules
What happens during anabolic reactions?
Simple subunit → Complex molecule
How do anabolic reactions take place?
In steps, coupled with ATP hydrolysis or another exergonic reaction.
State the ΔG of the following reaction:
glucose + 6O2 → 6CO2 + 6H2O
ΔG = -2870 kJ mol^-1
State the ΔG of the following reaction:
ATP + H2O → ADP + Pi
ΔG = -30.5 kJ mol^-1
State the ΔG of the following reaction:
glucose + fructose → sucrose
ΔG = +29.3 kJ mol^-1
State the ΔG of the following reaction:
glucose + ATP → glucose,p + ADP
ΔG = -16.7 kJ mol^-1
State the ΔG of the following reaction:
fructose + ATP → fructose,p + ADP
ΔG = -14.2 kJ mol^-1
State the ΔG of the following reaction:
glucose,p + fructose,p → sucrose + 2Pi
ΔG = -0.8 kJ mol^-1
