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23 Cards in this Set
- Front
- Back
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Enthalpy Change |
The amount of heat energy taken in or given out during any change in a system provided the pressure is constant |
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In an exothermic reaction heat is |
Given out |
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In an exothermic reaction the products have ______ energy than the reactants |
Less |
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In an exothermic reaction delta H is always |
Negative |
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In an endothermic reaction energy is |
Taken in |
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In an endothermic reaction the products have _____ energy than the reactants |
More |
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In an endothermic reaction delta H is |
Positive |
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What is the Standard Enthalpy of Formation
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The enthalpy change when one mole of the compound is formed from its elements under standard conditions with all reactants and products being in their standard states
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What is the Standard Enthalpy of combustion
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The enthalpy change when one mole of a substance is combusted completely in oxygen under standard conditions with all reactants and products being in their standard states
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What are the Standard conditions
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298K and 100kPa
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What is the Enthalpy of formation of an element
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0 kJ mol-1
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What is the equation for Energy Change
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Energy change (J) = mass of solution (g) x heat capacity (Jg-1K-1) x temperature change(K) Q= m x c x delta T |
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What is the Calorimetric Method
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One where substances are mixed in an insulated container and the temperature rise is measured
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How would you carry out a calorimetric experiment
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1)Wash the equipment with the solutions to be used 2) Dry the cup after washing 3) Put polystyrene cup in a beaker for insulation and support 4) Clamp thermometer into place making sure that the thermometer bulb is immersed in liquid 5) Measure the initial temperatures of the solution or both if two are used 6) Transfer reagent into the cup. If a solid reagent is used add the solution first 7) Stir Mixture 8) Measure final Temperature |
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why would it be difficult to obtain an exact temperature rise if the reaction is slow
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Because cooling occurs simultaneously with the reaction
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How is the problem of a slow reaction counteracted in a calorimetry experiment to obtain an exact temperature rise |
Extrapolate the temperature line backwards to the time where the reagents were added together
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What is the big error in the calorimetry experiment
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Heat loss reaction may be incomplete or slow |
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REMEMBER as it is assumed that all solutions have the same density as water e.g. 25cm3 will weigh
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25g
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When using delta H = Q/n what MUST be remembered
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to divide Q by 1000 to give you kj mol-1
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After calculating H=Q/n what must you remember to do
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Put the sign to represent the energy change. IF EXOTHEMIC THE SIGN IS NEGATIVE
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State Hess's Law
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The total enthalpy change for a reaction is the same regardless of the route taken `
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What is the definition for Mean Bond Energies
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The Mean Bond Energy is the enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules
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