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16 Cards in this Set
- Front
- Back
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Enthalpy change |
The change in energy as reactants turns into products. This is symbolized by delta H 'Delta'means the change in 'H' means stored heat energy. |
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Exothermic reactions |
Energy is released by the system and goes into the surroundings. Less energy is absorbed from the surroundings The reactants have higher energy than the products ,thus surroundings increase in temperature The value of delta H is negative |
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Endothermic reactions |
Energy is absorbed from the surroundings by the system.
The products have higher energy than the reactants .
The system is warmed up The value of delta H is positive |
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Three formats used to communicate enthalpy change |
1.Thermochemical equation with delta H as a product 2.Thermochemical equation with delta H as a separate term 3.Potential energy diagram |
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Thermochemical equation |
This is a balanced chemical equation with the energy on the product side . Example: N2 + 3H2 ------> 2NH3 + 92kj |
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Thermochemical equation with delta H as a separate form |
N2 + 3H2------> 2NH3 delta H= -92KJ |
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Calculating the quantity of heat |
Q=mcdeltaT 1joule=1000 KJ always convert to joule 1L =1000mL
%error= (theoretical value- experimental value )÷theoretical value×100
Units for measuring heat is always KJ.
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Specific heat capacities |
The units of heat capacities are J/g/°C. Heat capacity is the amount of heat needed to heat 1g of substance by 1°C Solids have lower specific heat capacities than liquids. Use GUESS format for solving problems. G- given U- unknown E- equation S- substitute S- solve |
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Formula for conversation |
n=m/M
1000mL=1L
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Difference between ' bomb' calorimeter and calorimeter that already has a heat soutce |
In a bomb calorimeter heat from the reaction is transferred to the metal chamber and to the water,but not beyond . Heat does not escape into the air. Heat escapes from a calorimeter with heat source. . |
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Calorimetry |
Calorimetry is the process of determining the heat lost or gained by an experiment. |
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Calorimeter |
A calorimeter is a device used to allow someone to experimentally make measurements as some endothermic or exothermic reactions occur. |
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HESS law |
This method is used when the delta H for reactions could not be calculated using the calorimetry system. The main equation is the target equation. Sometimes you'll have to add two or more given equations to arrive at your delta H value. Note the equations added must sum up to your target equation. Sometimes reversing an equation is possible too. When reversing an equation you have to reverse the sign of the delta H value also. |
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Heats of formation |
This is another method used to determine the enthalpy change a reaction. Delta H= the sum of delta H° (products)+the sum of delta H° for (reactants) |
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Hybrid cars |
Hybrids were invented by Geoffrey Ballard. Hybrids has both an electric and gasoline engine The energy emitted by these cars is clean They have regenerative breaking which allow less energy consumption Great city mileage Advantage is that they are expensive to maintain and to replace a damage part can be hard since they don't have much part for those type of cars on the market. |
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Rates of reaction |
Rate means how quickly or slowly something happens. The independent variable is time and the dependent variable is quantity. This is so because the quantity reacted is dependent on the amount of time passed. Rate =delta(×)÷delta t. So this means concentration or amount divided by time equals rate at which reaction occurred. Square brackets must be used to enclose concentration in chemistry. A spectrophotometre is used to measure when substances are dissolved in liquids. A special probe is used to measure the electrical conductivity of a solution at set intervals. There are two different rates to be considered.: The instantaneous rate -thisbis the rate at a certain point in time. This is found by drawing a tangent to the curve at a specified time. The Average rate- the rate for a given period of time. The time may be an entire reaction or it may be the first few seconds. These are classified as using the slope formula. Positive slopes means products forming (concentration increases with time. Negative means reactants. When finding instantaneous or average rate rate= delta (×) Rise ------------------ ÷ delta (t) Run THEN Rate = (A)2-(A)1 --------------- T2-T1 -------------------- T2-T1 |
