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51 Cards in this Set
- Front
- Back
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Heat |
a form of energy that flows from something at a higher temperature to something at a lower temperature |
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Temperature |
a measure of the average kinetic energy of particles |
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Internal energy |
the total amount of energy (kinetic and potential) in a sample of a substance. |
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What words do you use to describe the two things involved in the happenings of energy flow in chemical reactions? |
System and surroundings |
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System |
Our chemical reaction |
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Surroundings |
Everything else in the universe |
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Exothermic reaction |
heat energy is transferred from a system (chemical reaction) to the surroundings - the surroundings get hotter |
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Endothermic reaction |
A system (chemical reaction) takes in heat energy from the surroundings - the surroundings get cooler |
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Enthalpy change |
Is the heat energy exchanged with the surroundings at a constant pressure |
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Delta means |
a change in quantity |
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DeltaH values are usually quoted under |
standard conditions |
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The heat released in an exothermic reaction comes from... |
the decrease in internal energy (the total energy of all the particles) of the system, for example through the creation of chemical bonds (conversion of chemical energy to heat energy). |
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The heat energy consumed in an endothermic reaction... |
is converted to internal energy, for example through the breaking of chemical bonds (conversion of heat energy to chemical energy). |
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Enthalpy change of a system: |
The amount of heat energy change taken in/given out in a chemical reaction. |
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deltaH for an exothermic reaction is a --- value |
negative value |
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deltaH for an endothermic reaction is a --- value |
positive value |
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If we cannot measure the initial or final enthalpy of a system in a reaction shown in an enthalpy level diagram... |
There is no distinct scale on the vertical axis for the enthalpy level. We only know the change. |
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Total energy is --- in a chemical reaction |
conserved |
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The term stability is used to describe |
the relative energies of the reactants and products in a chemical reaction. If the products have less energy than the reactants then they are more stable |
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total energy of reactants = ... |
total energy of the products + heat given out |
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deltaH = ... |
enthalpy of products - enthalpy of reactants |
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enthalpy of a system can be regarded as essentially the .. |
total energy stored in a substance, basically the same as internal energy, not strictly true but good enough |
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Enthalpy changes have different values depending on the ... |
conditions under which they are measured |
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An enthalpy change under standard conditions is called |
a standard enthalpy change |
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standard enthalpy change symbol |
deltaH^phi where phi means 'under standard conditions' |
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Standard conditions are |
100 kPa (1.00 * 10^5 Pa) |
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--- Should always be specified for a standard enthalpy change |
Temperature (this can be written as deltaH^phi(298) or deltaH^phi(298K) |
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When temperature is not stated we will assume that |
the temperature is 298 K |
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Standard enthalpy change of reaction (deltaH^phi(r) is |
the enthalpy change (heat given out or heat taken in) when molar amounts of reactants, as shown in the stochiometric equation, react together under standard conditions to give the products |
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Standard enthalpy change of combustion symbols: |
ΔHθc |
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What is Standard Enthalpy Change Of Combustion? |
The enthalpy change when 1 mole of a substance is completely burnt in oxygen under standard conditions |
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A standard enthalpy change of combustion is always --- |
negative, because combustion is always an exothermic process |
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Specific heat capacity symbol |
c |
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Definition of specific heat capacity: |
The energy required to raise the temperature of 1g of a substance by 1 K (1 C) (or perhaps, be defined as the energy to raise the temperature of 1kg of susbtance by 1 K) |
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Amount of heat energy required is proportional to the --- and --- |
mass and temperature change |
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symbol for heat energy
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q |
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Equation for how much heat energy (q) must be supplied to raise the temperature of mass m by deltaTC(celsius symbol) |
q = mcDeltaT |
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The basic technique of measuring an enthalpy change of combustion is called |
calorimetry |
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Main flaw in practical experiments in the accuracy of measuring of enthalpy change? |
The loss of heat to surroundings, incomplete combustion |
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How could such a heat measuring experiment been improved? |
By determining the specific heat capacity of the can and taking this into account when doing the calculation, insulating the can so that less heat is lost to the surroundings, using some sort of draught shield to reduce convection currents around the experiment, ect. |
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What would these major flaws within the heat experiment be called? |
systematic errors |
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Incomplete combustion |
When there is insufficient oxygen to the flame |
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Minor problems of the heat experiment? |
Evaporation of the water and alcohol |
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A bomb calorimeter |
A heavily insulated piece of apparatus in which the substance is ignited electronically in a plentiful supply of oxygen. |
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General method for measuring enthalpy changes in solution: |
Measure out known reagants, record their initial temperatures, mix together the reagants in a polystere cup and record the minimum/maximum temperature observed. |
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The specific heat capacity of the final solution when measuring enthalpy changes in solution |
is assumed to be the same as water |
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Enthalpy change of neutralisation |
(deltaHn)the enthalpy change when one mole of water molecules are formed when an acid (H+) reacts with an alkali (OH-) under standard conditions: |
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The enthalpy change of neutralisation is always --- |
exothermic |
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Enthalpy change of solution |
(deltaHsol) is the enthalpy change when one mole of solution is dissolved in excess solvent to form a solution of 'infinite dilution' under standard conditions, eg: |
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The enthalpy change of a solution may be |
endothermic or exothermic |
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Infinite dilution means |
that any further dilution of the solution produces no further enthalpy change - i.e. the solute particles are assumed not to interact with each other in the solution |
