extra questions c8
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Explain why temp increases in an exothermic reaction until a certain point
• the temperature rises because the reaction is exothermic until 0.8 g (zinc) is added • (so) there is no additional reaction • (because) copper sulfate is used up
Explain why the volume of hydrogen collected in the measuring cylinder is less than the volume of hydrogen produced
hydrogen escapes from flask before the stopper is put on
Sulphur is produced in the reaction. Why does the mixture become cloudy
Sulphur is a solid and an insoluble substance
The diagram below shows a sealed flask of sodium hypochlorite and hydrochloric acid at equilibrium. Explain why equilibrium is reached in this reaction.
forward and reverse rates equal because no escape of reactants or products
The stopper in the diagram above is removed and hydrochloric acid is added. The stopper is replaced. Explain what happens to the equilibrium.
equilibrium shifts in favour of forward reaction to produce more of any products (new) equilibrium will be established
Explain the effect of increasing the pressure on this equilibrium.
no change because equal numbers of molecules
Describe how a reaction reaches equilibrium.
when a reversible reaction occurs in a sealed system when the forward and reverse reactions occur at (exactly) the same rate
A catalyst is used in the reaction. Explain how a catalyst increases the rate of a reaction.
• provides an alternative pathway • (which has) a lower activation energy
The methane gas will not burn in oxygen until a flame is applied, but once lit it continues to burn. Explain why energy must be supplied to start the reaction but it continues by itself once started.
• existing bonds must first be broken • molecules more likely to react when they collide) • more energy is released when new bonds form • exothermic • this breaks more bonds so the reaction continues
Describe what must happen to the molecules of ethanol and oxygen to allow them to react.
• to react particles must collide • with sufficient energy • (to cause) bond breaking
explain why percentage yield of sulphur trioxide (less moles) in this reaction is greater if the pressure is higher
• there are more moles of gas on the left • so the equilibrium shifts to the right
does adding a catalyst shift the position of equilibrium
no, it only increases the rate at which equilibrium is reached
the concentration of the substances to not change at dynamic equilibrium. explain why
the forward and reverse reactions are taking place at exactly the same rate
why does increasing temperature increase rate of reaction
• increasing the temperature increases the rate of reaction • (because) particles have more energy • (so) the frequency of collisions increases