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IGCSE CHEMISTRY
CHAPTER 6
| Question | Answer |
|---|---|
| The energy level diagram for the reaction between sodium hydrogen carbonate and dilute hydrochloric acid. Describes the type of reaction and the energy of the reactants and products? | Type of reaction - endothermic Energy of the reactants and products - the products have more energy than the reactants |
| The energy level diagram for the reaction between magnesium and hydrochloric acid. Name one statement about the reaction that is not correct? | The reaction is endothermic |
| The energy level diagram shows the energy of the reactants and products in a chemical reaction. Describes the energy change and the type of reaction. | Energy change - energy is given out to the surroundings Type of reaction - exothermic |
| Name one reaction that is endothermic? | Calcium carbonate decomposing when heated |
| Solid hydrated sodium carbonate was added to solid citric acid. The mixture was stirred and the temperature recorded every 10 seconds. Describes the reaction? | Reaction type - Neutralisation Energy change - Endothermic |
| A metal reacts with an aqueous solution. Describes the reaction? | Reaction - Combustion Energy Change - Exothermic |
| Name two statements about exothermic and endothermic reactions? | During an exothermic reaction, heat is given out Burning methane in the air is an exothermic reaction |
| What occurs when a fuel burns? | Fuel reacts with oxygen Energy change to exothermic |
| Some reactions are endothermic. How does the temperature and energy change in an endothermic reaction? | Temperature change decreases Energy taken in |
| Solutions of two chemicals are mixed. A reaction occurs and the temperature change is measured. What is the reaction? | If the reaction is endothermic, the temperature decreases and energy is taken in. |
| When ammonium nitrate is added to water the temperature of the water decreases. The ammonium nitrate can be recovered by evaporating the water added. Which explains these observations? | The ammonium nitrate dissolves in the water and the process is endothermic |
| Some white anhydrous copper(II) sulfate powder is put into a beaker of water and stirred. What would show that the process was exothermic? | The beaker feels warmer. |
| By striking the match, a chemical reaction takes place. Name one statements about the chemical reaction | Type of reaction - exothermic Reason - because energy is given out as the match burns |
| Acetylene, C2H2, is a hydrocarbon. When acetylene and oxygen react, the hot flame produced can be used to weld steel. Why does that happens? | Acetylene and oxygen react exothermically. |
| Which fuel needs oxygen in order to produce heat energy and which type of reaction produces the energy? | Fuel - Hydrogen Type of reaction - Exothermic |
| Some reactions are listed. methane + oxygen → carbon dioxide + water sodium + water → sodium hydroxide + hydrogen magnesium + hydrochloric acid → magnesium chloride + hydrogen What reaction is that? | Exothermic |
| Name one endothermic process? | Distilling petroleum |
| Name one that is not a endothermic process? | Obtaining lime from limestone |
| When an acid is added to an alkali the temperature rises. Describe this reaction? | Neutralisation and exothermic |
| Explain the phrase substitution reaction. | Hydrogen (atoms) replaced by (atoms) of a different element e.g. chlorine |
| How do photochemical reactions differ from other reactions? | Light required |
| Bond forming is exothermic, bond breaking is endothermic. Explain three differences between an exothermic reaction and an endothermic reaction. | Exothermic reaction gives out energy Endothermic reaction absorbs Takes in energy |
| Write an equation for the overall reaction occurring in the cell. | Zn + H2SO4 → ZnSO4 + H2 / Zn + 2H+ → Zn2+ + H2 |
| Explain why all cell reactions are exothermic and redox | Exothermic because a cell produces electrical energy/electricity |
| Which electrode, zinc or iron, is the negative electrode? Give two reason for your choice | Zinc It supplies electrons It forms ions more readily than iron |
| Suggest two ways of increasing the voltage of this cell | Replace zinc with magnesium Replace iron with copper |
| Some hydroxides, nitrates and carbonates decompose when heated. Name a metal hydroxide which does not decompose when heated | Any Group 1 metal |
| Write the equation for the thermal decomposition of copper(II) hydroxide | Cu(OH)2 → CuO + H2O |
| Suggest why these two hydroxides behave differently | Reactivity of metals Metals have different reactivities |
| Metal nitrates, except those of the Group 1 metals, form three products when heated. Name three products formed when zinc nitrate is heated | Zinc oxide, Nitrogen dioxide, Oxygen |
| Write the equation for the thermal decomposition of potassium nitrate | 2KNO3 → 2KNO2 + O2 |
| How is oxygen obtained from liquid air? | Fractional Distillation |
| Hydrogen and oxygen react to form water. 2H2 + O2 2H2O Give an example of bond breaking in the above reaction | Oxygen |
| Hydrogen and oxygen react to form water. 2H2 + O2 2H2O Give an example of bond forming in the above reaction | Bond between hydrogen and oxygen |
| Hydrogen and oxygen react to form water. 2H2 + O2 2H2O Is the change given in (i) exothermic or endothermic? | Endothermic |
| Give six reasons why hydrogen may be considered to be the ideal fuel for the future. | No pollution No CO No CO2 No oxides of nitrogen No greenhouse gases No global warming |
| Suggest a reason why hydrogen is not widely used at the moment. Name 6 points. | Obtaining hydrogen from water requires fossil fuels Storage problems Transport problems Limited range of vehicles available Methane as a source of steam reforming is finite Lack of distribution network |
| At equilibrium, only 1% of the hydrogen chloride exists as molecules, the rest has formed ions. In the other equilibrium, 97% of the hydrogen fluoride exists as molecules, only 3% has formed ions. What does this tell you about the strength of each acid? | Hydrogen chloride is a strong acid Hydrogen fluoride is a weak acid Weaker or stronger correctly applied for |
| (iii) How would the pH of two solutions differ? | Hydrogen chloride (aqueous) would have lower pH |
| What is an enzyme? | Biological catalyst |
| Pasteur said that fermentation was respiration in the absence of air. Suggest a definition of respiration | Production of energy (from food) by living “things” or by cells |
| On a large scale, the reaction mixture is cooled. Suggest a reason why this is necessary. | “kill” yeast or denature enzymes due to increase in temperature |
| Why does the fermentation stop? Suggest two reasons | All glucose used up Yeast “killed” or denatured or damaged by ethanol/alcohol |
| When the fermentation stops, there is a mixture of dilute aqueous ethanol and yeast. Suggest a technique which could be used to remove the cloudiness due to the yeast. | Filter |
| Name a technique which will separate the ethanol from the ethanol / water mixture. | Fractional distillation |
| Write a symbol equation for the action of heat on zinc hydroxide. | Zn(OH)2 = ZnO + H2O |
| Describe what happens when solid sodium hydroxide is heated strongly. | It would melt |
| What would be observed when copper(II) nitrate is heated? | blue (solid) to black (solid) to brown gas |
| What do you understand by the term equilibrium? | Rates equal; Concentrations do not change |
| When the equilibrium mixture is heated, it becomes a darker brown colour. Suggest if the reverse reaction is endothermic or exothermic. Give a reason for your choice | Endothermic and because this direction is favoured by high temperatures |
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Haridus Academy