https://padlet.com/hol_cjones/7rqixjqhco1q Made with knowledge en-us 2019-01-30 12:12:16 UTC 2024-01-06 00:34:53 UTC hello@padlet.com https://padlet-assets.s3.amazonaws.com/icons/Soccerball.png 317683 https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795113 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795113 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795114 If we add a solid to a solution and there is an enthalpy change we must work out how many moles of solid went into the solution.... OR... we use the volume and concentration of a solution to get the number of moles.
It is the chemical that isn’t in excess that is used to get n and then work out enthalpy changes. This chemical is said to be the limiting reagent.]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795114 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795115 Breaking bonds requires energy therefore it is endothermic.
Making bonds give out energy therefore it is exothermic.]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795115 317683 https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795116  ΔH = - mcΔt ÷ n
Units - Jmol^-1
M = mass of solution (g)
N= no. of moles that reacted
C= specific heat capacity - energy to heat 1g by 1 °C
ΔT - temperature change (°C)]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795116 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795117 The average bond enthalpy is the average value of the enthalpy required to break a covalent bond in a gaseous molecule.]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795117 317683 https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795118 Exothermic: ΔT positive and ΔH negative
Endothermic: ΔT negative and ΔH positive]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795118 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795120 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795120 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795121 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795121 317683 https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795122 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795122 317683 https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795123 Formation - arrows up
Breaking bonds - arrows down
Combustion - arrows up/down]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795123 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795124 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795124 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795125 The total enthalpy change for a reaction is independent of the route taken from reactants to product. ]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795125 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795126 The enthalpy change in a reaction (performed under standard conditions) between the number of moles of reactants shown in the chemical equation.]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795126 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795128 The enthalpy change when one mole of substance is formed from its constituent elements in their standard states (under standard conditions).]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795128 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795129 The enthalpy change when one mole of a substance is completely combusted in oxygen (under standard conditions).]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795129 317683 https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795130

Measure 50ml of acid using a burette and put it into the polystyrene cup

Make lid out of foil to prevent heat from escaping.

Accurately weigh out powdered solid 

Start the stopwatch

Use a thermometer to measure the starting temperature of the acid, multiple times to ensure a constant

Add the solid, stir until dissolved and put the lid back on quickly

Measure the temperature of the solution at regular intervals (30 seconds)  until the temperature begins to fall

Plot data on graph to calculate the change in temperature (Δt) 

ΔH= -mcΔt ÷ n for MgO

Repeat experiment for MgCO₃

ΔH₃ = ΔH₁ - ΔH₂

]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795130 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795131

The temperature is recorded for a few minutes before mixing to make sure it constants

The time of mixing (starting the reaction) is noted on the graph

The temperature is recorded for a number of minutes after mixing.

Lines are extended forward and back to the time of mixing. This is called extrapolating the data.

The temperature change is measured between the two extrapolated lines at the time of mixing.

]]> 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795131 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795132 2019-01-30 12:12:23 UTC https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795132 hol_cjones https://padlet.com/hol_cjones/7rqixjqhco1q/wish/325795134

Substances in standard states

Temperature = 298K (25°C)

Pressure = 1 atm (101,000 Pa) 

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