1830040
Description
Flashcards by Jem Kinney, updated more than 1 year ago
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Created by Jem Kinney
almost 10 years ago
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| Question | Answer |
| what is an exothermic reaction? | A reaction where energy is given out when bonds are formed. |
| What is an endothermic reaction? | A reaction where energy is taken in to break bonds. |
| what type of reaction is a neutralisation reaction? | an endothermic reaction because bonds are broken. |
| what type of reaction is a combustion reaction? | an exothermic reaction because bonds are formed. |
| is the statement "it is always the case that a reaction that is endothermic in one direction is exothermic in the other" true or false? | true. |
| what is the unit used to measure the enthalpy of combustion? | kilo-joules per mole (KJ mol -1) |
| why is the unit of measure kjmol-1 used? | Because it compares the same number of molecules for each fuel. |
| what unit is more important than the enthalpy change when measuring fuels? | the energy density (kJg-1) |
| what advantage does petrol have over alcohols? | It has a much larger energy density so there is more energy to be released in a tank. |
| what are the advantages and disadvantages of hydrogen gas? | it has a very high electron density however the low density of gas means a gram of hydrogen gas takes up a lot more space than a gram of liquid fuel would. therefore it is difficult to store hydrogen efficiently. |
| write a balanced equation for the combustion of hydrogen. | 2H2 + O2 > 2H2O |
| how do the products of combustion vary between hydrogen and other fuels? | no carbon dioxide is produced when hydrogen is burnt. |
| What is enthalpy change? | A measure of heat energy given out or taken in when a chemical or physical change occurs at constant pressure. |
| What are the standard conditions for measuring enthalpy change? | - pressure of 100 KPa - Temperature of 298K (25oc) |
| why is it important to have a standard pressure? | Pressure affects the amount of heat energy given out by reactions that involve gases. If a gas is given out, then some energy is required to push away the atmosphere. the greater the atmospheric, the more energy that is used for this. |
| what is the unit for the standard enthalpy change of reaction. | Kilojoules per mole, kJ mol -1 |
| What is the standard molar enthalpy of formation? | The standard molar enthalpy of combustion is the enthalpy change when one mole of substance is formed from its constituent elements under standard conditions, all reactants and products in their standard states. |
| what is the standard molar enthalpy of combustion? | The standard molar enthalpy change of combustion is the enthalpy change when one mole of substance is completely burned in oxygen under standard conditions, all reactants and products in their standard states. |
| What is temperature? | Temperature is related to the average kinetic energy of particles in a system. |
| what is heat? | Heat is a measure of the total energy of the particles present in a given amount of substance. |
| what is the equation to calculate enthalpy change? | q=mcΔT q= enthalpy change m= mass of substance c= specific heat capacity ΔT= change in temperature |
| What is calorimeter? | An instrument for measuring the heat changes that accompany chemical reactions |
| state 4 reasons why may simple calorimeter be inaccurate. | There may be draughts that take heat away from the calorimeter. Heat is lost from the top and sides of the calorimeter. The beaker an the rest of the apparatus itself gets heated rather than just the water. Not all the fuel could burn and in complete combustion could occur. |
| what is the most accurate way to measure enthalpies of combustion? | using a bomb calorimeter |
| What is Hess's law? | Hess's law states that the enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products |
| What is the standard enthalpy of elements? | The standard enthalpy of all elements in their standard states are taken as zero. |
| What is the bond dissociation enthalpy? | The enthalpy change required to break a covalent bond with all species in the gaseous state. |
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