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39 Cards in this Set
- Front
- Back
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How are particles in a solid arranged? |
Packed closely together Vibrate around fixed positions |
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How are particles in a liquid arranged? |
Particles are packed closely together, but can slip over each other in a random motion |
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How are the particles in a gas arranged? |
Move randomly Have lots of space between them |
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Give reasons for the limitations of the particle model: |
It assumes that substances are made up of solid spheres with no forces acting between them Substances are made up of atoms, molecules and ions, which are mostly empty space They are not solid spheres and have different sizes and shapes with forces between them |
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What changes occur to the particles of a gas as it is cooled to a temperature below its boiling point? |
Gas particles slow down and come closer together New intermolecular forces are formed between the particles Energy is given out This stops when all the gas has become liquid |
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What happens to particles when a solid is heated above its melting point? |
Solid particles absorb energy Energy is used to overcome strong forces of attraction between neighbouring particles They break away from their fixed positions and start moving around No temperature rise until all the particles have melted |
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Is energy transferred to or from the surroundings in melting/ boiling? |
From surroundings to the substance |
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Is energy transferred to or from the surroundings in condensation/ freezing? |
To the surroundings from substance |
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Why do substances have different melting and boiling points? |
Have different intermolecular forces between the particles |
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What is a mixture? |
A substance made up of two or more elements or compounds that are not chemically bonded together |
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What are 3 ways that mixtures are different to compounds? |
1) have no fixed composition 2) elements/ compounds can be easily separated 3) no chemical bonds between components of mixture |
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What main 4 techniques are used to separate mixtures? |
Filtration, crystallization, distillation, chromatography |
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When is filtration used? |
Insoluble solid from a solvent |
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How might you separate a soluble solid from a solution? |
By evaporation followed by crystallization. Slowly heat a solution in an evaporating basin to remove some of the solvent. Using a glass rod, dip the end of the rod into the solution and dab onto a white tile. If solution starts to crystalize, remove the basin from the heat and allow to cool. The salt will become insoluble in the cool highly concentrated solution and crystals will start to form. Filter the crystals out of solution and place in drying oven. |
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How can the process of distillation be used to remove dissolved impurities from a sample if water? |
Heat the mixture until boiling. Evaporated solvent passes down condenser and the vapour is cooled below its boiling point and condenses. Any dissolved solid will remain in the flask. |
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What is an acid? |
Substance that produces H+ ions when added to water Eg: HCl, HNO3, H2SO4 |
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What is a base? |
Substance that will neutralise an acid Eg: metal oxide, metal hydroxide |
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How is an alkali different to a base? |
Alkali is a soluble base. Produce OH- ions when added to water Eg: metal hydroxide |
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What is the general equation for a neutralisation reaction? |
Acid + alkali -> salt + water |
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What is the ionic equation for neutralisation? |
H+ + OH- -> H2O |
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What pH is neutral? |
pH7 |
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What range of pH is alkali? |
8-14 |
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What is the product of reaction between hydrogen and hydroxide ions? |
Water |
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pH of 4.2 us? |
Acidic |
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Lithium hydroxide (alkali) reacts with hydrochloric acid A) what type of reaction is this? B) what is formed in this reaction? |
A) neutralisation B) salt (lithium chloride) + water |
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What are the 4 main neutralisation reactions? |
Acid + alkali Metal + acid Metal oxide + acid Metal carbonate + acid |
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What happens to the total energy in the universe during a chemical reaction? |
Stays the same as overall amount of energy in the reactants and surroundings doesn't change- energy is conserved |
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What do you call a reaction that transfers energy to its surroundings? |
Exothermic |
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What do you call a reaction that takes in energy from its surroundings? |
Endothermic |
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Examples of exothermic reactions? |
Combustion Neutralisation Oxidation reactions |
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Examples of endothermic reactions? |
Thermal decomposition Electrolysis Photosynthesis |
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What is an example of an everyday use of an endothermic reaction? |
Sports injury packs- takes in heat and the chemicals become very cold, removing heat from to the site of the injury |
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A) How would you measure the energy released by a chemical reaction between two solutions? B) what is one common error with this experiment? |
A) Measure the volume of known solutions and record the starting temperatures. Pour both solutions into an insulating polystyrene cup and stir. Observe the temperature of the mixture and record the max temperature it reaches B) energy lost to the surroundings |
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What is the activation energy? |
Minimum amount of energy the reactant particles need to collide with each other to start a reaction |
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Is breaking bonds exo or endothermic? |
Endothermic |
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What energy change takes place when new bonds are formed? |
Exothermic |
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Why is energy released to surroundings during exothermic reaction? |
Energy released by bond formation is greater than the energy used to break bonds |
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What is the bond energy of a chemical bond? |
Amount of energy required to break a bond (or released when is made) |
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How do you calculate energy change of reaction? |
Energy change = energy of bond breaking - energy of bond making |
