Experiments
What is the visual indication of reaction progress in an experiment with sodium thiosulfate and hydrochloric acid?
Formation of a precipitate
What type of energy does a catalyst affect?
Activation energy
What is an exothermic reaction?
A chemical reaction that releases energy to the surroundings.
What is the oxidation number of Cr in K2Cr2O7?
+6
What is the name of group 1 elements?
Alkali metal
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If the concentration of hydrochloric acid is doubled, what happens to the rate of reaction with magnesium?
It doubles.
What is the sign of enthalpy change of combustion? positive or negative?
negative
What happens to the substance in an oxidation reaction?
its oxidation number increases/ it loses electrons/ it gains oxygen.
What is the trend of melting points of halogens down the group?
increase
What gas is produced when calcium carbonate reacts with hydrochloric acid?
Carbon dioxide/ CO2
What happens to the reaction rate at very low temperatures?
It slows down./ Decreases.
How does an endothermic reaction affect the temperature of surroundings?
The temperature of surroundings decreases.
Who got oxidized? 2Na + Cl2 = 2NaCl
Na
What is the color of bromine water?
Br2(aq)
orange-brown/ brown
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What is the catalyst?
Catalyst is a substance that speeds up the rate of reaction but chemically unchanged.
Define bond enthalpy (energy)
The energy required to break 1 mole of a bond in gaseous state.
Is it a redox reaction?
NaHCO3 + CH3COOH = CH3COONa + CO2 + H2O
No
State one application of helium.
What observation is made when magnesium reacts with hydrochloric acid?
bubbles
Which reacts faster: solid chips or powdered solids?
powdered solids
In a Hess’s Law, what happens if you reverse a reaction?
The enthalpy change sign must be reversed.
Zn + CuCl2 = ZnCl2 + Cu
Which one is oxidising agent?
CuCl2
State three chemical properties of most transition metals.
2. act as catalysts
3. have variable oxidation numbers