Thermodynamics 2 Flashcards
What is heat capacity (C) ?
- The amount of heat required to raise the temperature of an object or substance a given amount by 1°C.
What is Molar Heat Capacity (Cm) ?
- The amount of heat required to raise the temperature of 1 mol of a substance by 1 °C
Calorimetry and Heat Capacity
- Measure the heat flow at constant volume (∆E).
Heat capacity equation
q = C x ∆T (q: quantity of heat)
Molar Heat Capacity (Cm) equation
q = (Cm) x (moles of substance) x ∆T
What is specific heat ?
- The amount of heat required to raise the temperature of 1 g of a substance by 1 °C.
Specific heat equation
- q = (specific heat) x (mass of substance) x ∆T
Differential Scanning Calorimetry
(DSC)
- measures difference in heat transferred to
and from sample in comparison to reference material
Hess’s law
- The overall enthalpy change for a reaction is equal to the sum of the enthalpy changes for the individual steps in the reaction
Haber Process
- 3H2(g) + N2(g) 2NH3(g)
- ∆H° = -92.2 kJ
Standard Enthalpy of Formation (ΔH0)
- the heat change that results when one mole of a compound is formed from its elements at a pressure of 1 atm
What is the standard enthalpy of formation of an element in its stable form ?
- the standard enthalpy of formation of any element in its most stable form is zero.
Standard Heat of Formation (∆H°f )
- enthalpy change for the formation of 1 mol of a substance in its standard state from its constituent elements in their standard states
Is breaking bonds (dissociation) endothermic or exothermic ?
- endothermic
Is making new bonds (association) endothermic or exothermic ?
- exothermic
Bond Dissociation Energy
- amount of energy that must be supplied to break a chemical bond in an isolated molecule in the gaseous state
- thus the amount of energy released when the bond forms
What do exact bond enthalpy values depend on ?
- bond order
- electronic environment of the 2 atoms compromising the bond
Equation for calculating ΔH using bond enthalpies ?
- ΔH = Bonds Broken − Bonds Formed
Standard Enthalpies of Combustion, ΔHc
- Standard change in enthalpy per mole of combustible substance
Equation for calculating standard enthalpies of combustion ?
- ΔH = Bonds Broken − Bonds Formed
- arrows go down
What is a spontaneous processes ?
- A process that, once started, proceeds on its own without a continuous external influence.
18–20-year-old males require…..
~12 MJ of energy input per day.
18–20-year-old females require
~9 MJ of energy input per day.
What is body temperature regulated by?
- radiation and perspiration.
State Function
- A function or property whose value depends
only on the present state, or condition, of the system, not on the path used to arrive at that state.
Enthalpy Change (ΔH)
-The heat change in a reaction or process at constant pressure; ΔH = ΔE + PΔV.
Entropy (S)
- The amount of molecular randomness in a system
What are spontaneous processes favoured by?
- Favoured by a decrease in H (negative ∆H).
- Favoured by an increase in S (positive ∆S).
What are non spontaneous processes favoured by?
- Favoured by an increase in H (positive ∆H).
- Favoured by a decrease in S (negative ∆S).
