C3.1

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What reactions occur between fuels/foods and oxygen?
Exothermic reactions. Calorimeter can be used to measure the amount of energy released when substances burn (in joules or calories - 1 cal = 4.2J).
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Describe the simplest calorimeter.
Doesn’t give accurate results as energy released heats surroundings but results can be used for comparison of energy released by diff fuels. Water in glass beaker/metal can. Temp rise of water depends on amount of energy released when substance burns
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How can a simple calorimeter be used to compare the energy released by burning different substances?
The energy change in kJ per gram or per mole. Energy change in kJ/mol calculated by multiplyingthe energy change in kJ/g byt the relative formula mass of the substance.
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What is the equation used to calculate the amount of energy transferred to the water in joules?
Q (amount of energy transferred in J) = M(*** of water in grams) × c(specific heat capacity of water J/g=C) × T (temp change in oC).
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What happens when a reaction takes place in a solution?
Energy is transferred to or from the solution. We can do the reactions in an insulated container to reduce energy transfers to the surroundings. When we calculate the energy change we assume that c=4.2J/goC + M= 1cm3=1g.
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What is the difference between endothermic and exothermic reactions?
Breaking bonds is endothermic because energy is taken in __()-- + so exothermic changes go up and exothermic changed go down--()__ as when new bonds in the product are formed energy is released + this is exothermic.
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What are catalysts and what is activation energy?
Catalysts increase rata of reaction by providing a diff pathway with a lower activation energy – by lowering the ‘minimum energy needed for the reaction to happen’.
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What makes an overall reaction endothermic or exothermic?
Energy is needed in chemical reactions to break bonds in the reactants. Energy is released when new bonds are formed in the products + it’s the difference in these energy changes – energy taken in in endothermic reaction, energy released in exothermi
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What is bond energy (measured in kJ/mol)?
Energy needed to break bond between two atoms. An equal amount of energy released when a bond forms between 2 atoms. We can use bond energies to calculate the overall energy change for a reaction.
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A balanced equation for the reaction is needed to calculate the energy change for a reaction. What do you then calculate?
Total amount of energy needed to break all bonds in reactants. Total amount of energy released in making all bonds in products. Difference between 2 totals.
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What are advantages of using hydrogen as a fuel?
Burns easily + releases a large amount of energy per gram. Produces no CO2 when burned only H2O. Produced from renewable sources + can be burned in combustion engines or used in fuel cells to power vehicles.
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What are the disadvantages of using hydrogen as a fuel cell?
Supply, storage and safety problems. Vehicles that use fuels cells need to match the performance, convenience + costs of petrol/diesel.
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Other cards in this set

Card 2

Front

Describe the simplest calorimeter.

Back

Doesn’t give accurate results as energy released heats surroundings but results can be used for comparison of energy released by diff fuels. Water in glass beaker/metal can. Temp rise of water depends on amount of energy released when substance burns

Card 3

Front

How can a simple calorimeter be used to compare the energy released by burning different substances?

Back

Preview of the front of card 3

Card 4

Front

What is the equation used to calculate the amount of energy transferred to the water in joules?

Back

Preview of the front of card 4

Card 5

Front

What happens when a reaction takes place in a solution?

Back

Preview of the front of card 5
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